All Exams > Class 9 > Science Class 9 > All Questions
All questions of Atoms and Molecules for Class 9 Exam
Which constituent of air is monoatomic?- a)Argon
- b)Water vapour
- c)Oxygen
- d)Nitrogen
Correct answer is option 'A'. Can you explain this answer?
Which constituent of air is monoatomic?
a)
Argon
b)
Water vapour
c)
Oxygen
d)
Nitrogen
 | Avinash Patel answered |
Argon is a Noble gas. Noble gases are not very reactive since they have a very stable electron configuration. It is only about 1% of the air in the atmosphere but it is more abundant than any other element on the Periodic Table behind Nitrogen and Oxygen.
What are the building blocks of matter?- a)Compound
- b)Molecules
- c)Atoms
- d)Element
Correct answer is option 'C'. Can you explain this answer?
What are the building blocks of matter?
a)
Compound
b)
Molecules
c)
Atoms
d)
Element
 | Molik answered |
Atoms are building blocks
Which one of the following is the modern symbol of Gold?- a)Gl
- b)Go
- c)Si
- d)Au
Correct answer is option 'D'. Can you explain this answer?
Which one of the following is the modern symbol of Gold?
a)
Gl
b)
Go
c)
Si
d)
Au
| | Arvind Singh answered |
Gold is a chemical element with symbol Au (from Latin: aurum) and atomic number 79, making it one of the higher atomic number elements that occur naturally. In its purest form, it is a bright, slightly reddish yellow, dense, soft, malleable, and ductile metal.
Can you explain the answer of this question below:Which is the smallest particle of an element that can take part in a chemical reaction?
- A:
Molecule
- B:
Mixture
- C:
Compound
- D:
Atom
The answer is d.
Which is the smallest particle of an element that can take part in a chemical reaction?
Molecule
Mixture
Compound
Atom
| | Arvind Singh answered |
The basic unit of matter is the atom. It is the smallest particle of an element which can take part in chemical reactions and may or may not exist separately. It consists of sub-atomic particles, i.e., protons, neutrons and electrons.
The number of atoms present in one molecule of an element is called as:- a)Empirical formula
- b)Molecule
- c)Atomicity
- d)Compound
Correct answer is option 'C'. Can you explain this answer?
The number of atoms present in one molecule of an element is called as:
a)
Empirical formula
b)
Molecule
c)
Atomicity
d)
Compound
 | Learning Enablers answered |
Atomicity is the total number of atoms present in one molecule of an element or a compound. For example: one molecule of hydrogen (H2) contains two atoms of hydrogen. Therefore, atomicity of hydrogen is 2. Simialrly, 1 molecule of O3 contains 3 atoms. Therefore, its atomicity is 3. molecule of Argon exist as Ar and hence its a monoatomic compound.
The number of moles for 52g of He is:
(Atomic Mass of He: 4u)- a) 6.022 × 1023
- b)13
- c)52
- d)1
Correct answer is option 'B'. Can you explain this answer?
The number of moles for 52g of He is:
(Atomic Mass of He: 4u)
(Atomic Mass of He: 4u)
a)
6.022 × 1023
b)
13
c)
52
d)
1
 | Learners Habitat answered |
Gram atomic mass of He = 4u
Therefore 52 g of He contains :
= 52 / 4
= 13 moles
Therefore 52 g of He contains :
= 52 / 4
= 13 moles
One atomic mass unit is a mass unit equal to exactly one twelfth (1/12th) the mass of one atom of ___________.- a)Carbon-12
- b)Nitrogen -14
- c)Carbon-1
- d)4.Silicon-14
Correct answer is option 'A'. Can you explain this answer?
One atomic mass unit is a mass unit equal to exactly one twelfth (1/12th) the mass of one atom of ___________.
a)
Carbon-12
b)
Nitrogen -14
c)
Carbon-1
d)
4.Silicon-14
 | Jyoti Kapoor answered |
An atomic mass unit (symbolized AMU or amu) is defined as precisely 1/12 the mass of an atom of carbon-12. The carbon-12 (C-12) atom has six protons and six neutrons in its nucleus. In imprecise terms, one AMU is the average of the proton rest mass and the neutron rest mass.
NaCl molecule is made of which of the following ions?- a)Na cation and Cl anion
- b)Cl cation and Na anion
- c)Both Na and Cl cation
- d)Both Na and Cl anion
Correct answer is option 'A'. Can you explain this answer?
NaCl molecule is made of which of the following ions?
a)
Na cation and Cl anion
b)
Cl cation and Na anion
c)
Both Na and Cl cation
d)
Both Na and Cl anion
| | Jyoti Kapoor answered |
An oxygen molecule (O2) is a good example of a molecule with a covalent bond. Ionic bonds occur when electrons are donated from one atom to another. Table salt (NaCl) is a common example of a compound with an ionic bond.
How do atoms usually exist in nature?- a)In the form of molecules
- b)In the form of ions
- c)In the free state
- d)In the form of molecules and Ions
Correct answer is option 'D'. Can you explain this answer?
How do atoms usually exist in nature?
a)
In the form of molecules
b)
In the form of ions
c)
In the free state
d)
In the form of molecules and Ions
 | Khushi answered |
Most of the elements in environment do not have 8 electrons in their valance shells(because of which they are more or less reactive and unstable ) so they react with the atoms of other metals to form molecules or ion to achieve noble gas configuration and become stable. The atoms of only a few elements like helium , Neon ..etc have their valance shells already filled with 8 electrons.so they can exist in free state. But matter mostly exist in the form of molecules and ions.
Valency of Calcium element is:- a)4
- b)5
- c)2
- d)3
Correct answer is option 'C'. Can you explain this answer?
Valency of Calcium element is:
a)
4
b)
5
c)
2
d)
3
| | Amit Sharma answered |
The valency of Calcium of 2+. Calcium has 2 electrons in its outermost shell, its electronic configuration being (2,8,8,2). In order to attain stability it loses 2 electrons to become stable according to the octet rule.
The reaction used in the experiment to verify the law of conservation of masses is included in which of the following categories?
AgNO3(aqueous) + KCl(aqueous) —–AgCl(precipitate) + KNO3(aqueous)- a)Precipitation reaction
- b)Double displacement reaction
- c)Neutralization reaction
- d)Both A and B
Correct answer is option 'D'. Can you explain this answer?
The reaction used in the experiment to verify the law of conservation of masses is included in which of the following categories?
AgNO3(aqueous) + KCl(aqueous) —–AgCl(precipitate) + KNO3(aqueous)
AgNO3(aqueous) + KCl(aqueous) —–AgCl(precipitate) + KNO3(aqueous)
a)
Precipitation reaction
b)
Double displacement reaction
c)
Neutralization reaction
d)
Both A and B
 | Imk Pathshala answered |
The correct answer is D: Both A and B.
- Precipitation Reaction: AgNO3(aq) + KCl(aq) → AgCl(s) + KNO3(aq) forms a solid precipitate.
- Double Displacement Reaction: AgNO3(aq) + KCl(aq) → AgCl(s) + KNO3(aq) involves the exchange of ions between two compounds.
- Explanation: The given reaction demonstrates both characteristics, forming a precipitate (A) and involving double displacement of ions (B), making it both a precipitation and a double displacement reaction.
- Precipitation Reaction: AgNO3(aq) + KCl(aq) → AgCl(s) + KNO3(aq) forms a solid precipitate.
- Double Displacement Reaction: AgNO3(aq) + KCl(aq) → AgCl(s) + KNO3(aq) involves the exchange of ions between two compounds.
- Explanation: The given reaction demonstrates both characteristics, forming a precipitate (A) and involving double displacement of ions (B), making it both a precipitation and a double displacement reaction.
Cl2 stands for:- a)2 molecules of chlorine
- b)2 atoms of chlorine
- c)2 ions of chlorine
- d)3 molecule of chlorine
Correct answer is option 'B'. Can you explain this answer?
Cl2 stands for:
a)
2 molecules of chlorine
b)
2 atoms of chlorine
c)
2 ions of chlorine
d)
3 molecule of chlorine
 | Ravi Verma answered |
Cl’ represents one chlorine atom. It is found in nature in diatomic form as a molecule I.E. ,Cl2.
5 grams of compound A reacts with 10 grams of compound B to produce a new compound C. What should be the mass of C according to law of conservation of mass?- a)15 g
- b)5 g
- c)50 g
- d)10 g
Correct answer is option 'A'. Can you explain this answer?
5 grams of compound A reacts with 10 grams of compound B to produce a new compound C. What should be the mass of C according to law of conservation of mass?
a)
15 g
b)
5 g
c)
50 g
d)
10 g
| | Anita Menon answered |
As from law of conservation of mass:-mass of reactants=mass of productTherefore, mass of compound A + mass of compound B=mass of compound CSo, 5g + 10g= 15g
Which atom is the smallest atom of all?- a)Lithium
- b)Helium
- c)Hydrogen
- d)Carbon
Correct answer is option 'C'. Can you explain this answer?
Which atom is the smallest atom of all?
a)
Lithium
b)
Helium
c)
Hydrogen
d)
Carbon
| | Gayatri Deshpande answered |
Explanation:
Factors Affecting Atomic Radius:
Comparison of Atomic Radii:
Conclusion:
The size of an atom is determined by its atomic radius, which is the distance from the center of the nucleus to the outermost electron. Therefore, the smallest atom will have the smallest atomic radius.
Factors Affecting Atomic Radius:
- Number of protons in the nucleus
- Number of energy levels or electron shells
- Effective nuclear charge
Comparison of Atomic Radii:
Based on the factors affecting atomic radius, we can compare the atomic radii of the four given elements:
- Hydrogen has only one proton and one electron, making it the smallest atom.
- Helium has two protons and two electrons, making it slightly larger than hydrogen.
- Lithium has three protons and electrons, and is larger than both hydrogen and helium.
- Carbon has six protons and electrons, and is larger than all three previous elements.
Conclusion:
Therefore, the smallest atom of all is Hydrogen, with only one proton and one electron.
The atomic masses and chemical properties of Sulphur and Phosphorus are different. This can be explained on the basis of:- a)Law of conservation of mass
- b)Laws of Chemical combination
- c)Law of constant proportions
- d)Dalton’s Atomic theory
Correct answer is option 'D'. Can you explain this answer?
The atomic masses and chemical properties of Sulphur and Phosphorus are different. This can be explained on the basis of:
a)
Law of conservation of mass
b)
Laws of Chemical combination
c)
Law of constant proportions
d)
Dalton’s Atomic theory
 | Sowmya answered |
Dalton according to Dalton's theory he says that compounds are combinations of two or more different types of atoms.
Who gave the Law of constant proportions?- a) Cavendish
- b) Proust
- c) Dalton
- d) Lavoisier
Correct answer is option 'B'. Can you explain this answer?
Who gave the Law of constant proportions?
a)
Cavendishb)
Proustc)
Daltond)
Lavoisier| | Arvind Singh answered |
A molecule of water will always have two hydrogen atoms and one oxygen atom, meaning that in a bottle of pure water the hydrogen to oxygen atom ratio will always be 2:1. This seems very logical to us today. But 300 years ago, scientists didn't understand compounds this way. However, in 1794, Joseph Proust published the Law of Constant Proportions, which says that a chemical molecule will always contains the same elements in the same proportion.
There are two parts to the law of constant proportions: 1) there will always be the same elements that make up a compound, and 2) the mass of these compounds will always be in the same proportion.
Which of the following is anion?
A. Magnesium
B. Sulphate
C. Oxalate
D. Ammonium- a)(a) and (b) are correct
- b)(a), (b) and (c) are correct
- c)(b) and (c) are correct
- d)All of these
Correct answer is option 'C'. Can you explain this answer?
Which of the following is anion?
A. Magnesium
B. Sulphate
C. Oxalate
D. Ammonium
A. Magnesium
B. Sulphate
C. Oxalate
D. Ammonium
a)
(a) and (b) are correct
b)
(a), (b) and (c) are correct
c)
(b) and (c) are correct
d)
All of these
 | Aditi Uppal answered |
Anions means negatively charged ions .Therefore , (c) is the correct option .
Calculate the formula unit mass of ZnCl2?- a)136.3 u
- b)124 u
- c)123 u
- d)111 u
Correct answer is option 'A'. Can you explain this answer?
Calculate the formula unit mass of ZnCl2?
a)
136.3 u
b)
124 u
c)
123 u
d)
111 u
 | Kavya Nambiar answered |
Formula mass unit is calculatedin same way as molecular mass.
so,zncl2= 65.3+35.5 x 2
= 65.3+71
=136.3
Valency of hydrogen is 1 and that of sulphur is 2. What should be the formula of hydrogen sulphide?- a)HS
- b)H2S2
- c)HS2
- d)H2S
Correct answer is option 'D'. Can you explain this answer?
Valency of hydrogen is 1 and that of sulphur is 2. What should be the formula of hydrogen sulphide?
a)
HS
b)
H2S2
c)
HS2
d)
H2S
| | Jyoti Kapoor answered |
Hydrogen sulfide is the chemical compound with the chemical formula H2S. It is a colorless gas with the characteristic foul odor of rotten eggs. It is very poisonous, corrosive, and flammable.
Molecules can exist in free state because:- a)They are very stable.
- b)They are electrically charged.
- c)They are very reactive.
- d)They are bigger in size as compared to atoms.
Correct answer is option 'A'. Can you explain this answer?
Molecules can exist in free state because:
a)
They are very stable.
b)
They are electrically charged.
c)
They are very reactive.
d)
They are bigger in size as compared to atoms.
 | Raghavendra Jain answered |
The answer to the given question is option 'A': Molecules can exist in a free state because they are very stable.
Explanation:
Molecules are formed when two or more atoms chemically combine by sharing electrons or through other types of bonding. These atoms can be from the same element or different elements. The resulting molecule has a stable structure due to the sharing or transfer of electrons, which allows the atoms to achieve a more stable electron configuration. Here is a detailed explanation of why molecules are stable and can exist in a free state:
1. Stable electron configuration:
Molecules are formed when atoms combine in such a way that they achieve a stable electron configuration. This stability is achieved by filling or emptying their outermost energy level, also known as the valence shell. By sharing or transferring electrons, atoms can achieve a full valence shell, which is a highly stable configuration. This stable electron configuration contributes to the stability of molecules.
2. Strong chemical bonds:
Molecules are held together by strong chemical bonds, such as covalent bonds or ionic bonds. Covalent bonds involve the sharing of electrons between atoms, while ionic bonds involve the transfer of electrons from one atom to another. These bonds are formed through the attraction between positively charged nuclei and negatively charged electrons. The strength of these bonds contributes to the stability of molecules.
3. Low potential energy:
Molecules have lower potential energy compared to individual atoms. When atoms combine to form a molecule, the resulting structure has a lower energy state. This decrease in potential energy is due to the formation of chemical bonds, which release energy. The lower potential energy of molecules makes them more stable and allows them to exist in a free state.
4. Balanced forces:
In a molecule, the attractive forces between atoms (chemical bonds) are balanced by repulsive forces between electrons and between nuclei. This balance of forces helps maintain the structure of the molecule and prevents it from easily breaking apart. The balanced forces contribute to the stability of molecules in a free state.
Conclusion:
In conclusion, molecules can exist in a free state because they are very stable. This stability is due to their stable electron configuration, strong chemical bonds, low potential energy, and balanced forces. These factors work together to maintain the integrity of the molecule and prevent it from easily dissociating into its constituent atoms.
Explanation:
Molecules are formed when two or more atoms chemically combine by sharing electrons or through other types of bonding. These atoms can be from the same element or different elements. The resulting molecule has a stable structure due to the sharing or transfer of electrons, which allows the atoms to achieve a more stable electron configuration. Here is a detailed explanation of why molecules are stable and can exist in a free state:
1. Stable electron configuration:
Molecules are formed when atoms combine in such a way that they achieve a stable electron configuration. This stability is achieved by filling or emptying their outermost energy level, also known as the valence shell. By sharing or transferring electrons, atoms can achieve a full valence shell, which is a highly stable configuration. This stable electron configuration contributes to the stability of molecules.
2. Strong chemical bonds:
Molecules are held together by strong chemical bonds, such as covalent bonds or ionic bonds. Covalent bonds involve the sharing of electrons between atoms, while ionic bonds involve the transfer of electrons from one atom to another. These bonds are formed through the attraction between positively charged nuclei and negatively charged electrons. The strength of these bonds contributes to the stability of molecules.
3. Low potential energy:
Molecules have lower potential energy compared to individual atoms. When atoms combine to form a molecule, the resulting structure has a lower energy state. This decrease in potential energy is due to the formation of chemical bonds, which release energy. The lower potential energy of molecules makes them more stable and allows them to exist in a free state.
4. Balanced forces:
In a molecule, the attractive forces between atoms (chemical bonds) are balanced by repulsive forces between electrons and between nuclei. This balance of forces helps maintain the structure of the molecule and prevents it from easily breaking apart. The balanced forces contribute to the stability of molecules in a free state.
Conclusion:
In conclusion, molecules can exist in a free state because they are very stable. This stability is due to their stable electron configuration, strong chemical bonds, low potential energy, and balanced forces. These factors work together to maintain the integrity of the molecule and prevent it from easily dissociating into its constituent atoms.
Can you explain the answer of this question below:Which of the following is correct pair of elements and its symbol?
- A:
Silver – Si
- B:
Sodium – So
- C:
Potassium – Pt
- D:
Sulphur – S
The answer is d.
Which of the following is correct pair of elements and its symbol?
Silver – Si
Sodium – So
Potassium – Pt
Sulphur – S
 | Prachi Rathore answered |
Here are the righ pairs .......... ... silver-Ag ....... sodium-Na ...... potassium- K...... and sulphur - s so in the given options (D) sulphur - s. is right answer
Which of the following can be used to see atoms?- a)Scanning tunneling microscope
- b)Microscope
- c)Most powerful microscope
- d)Optical microscope
Correct answer is option 'A'. Can you explain this answer?
Which of the following can be used to see atoms?
a)
Scanning tunneling microscope
b)
Microscope
c)
Most powerful microscope
d)
Optical microscope
| | Jyoti Kapoor answered |
A scanning tunneling microscope (STM) is an instrument for imaging surfaces at the atomic level. Its development in 1981 earned its inventors, Gerd Binnig and Heinrich Rohrer (at IBM Zrich), the Nobel Prize in Physics in 1986. For an STM, good resolution is considered to be 0.1 nm lateral resolution and 0.01 nm (10 pm) depth resolution.With this resolution, individual atoms within materials are routinely imaged and manipulated. The STM can be used not only in ultra-high vacuum but also in air, water, and various other liquid or gas ambients, and at temperatures ranging from near zero kelvin to over 1000 DEGC.
9 grams of water decompose to give:- a)4g oxygen and 16g hydrogen
- b)2g hydrogen and 1g oxygen
- c)8g oxygen and 1g hydrogen
- d)none
Correct answer is option 'C'. Can you explain this answer?
9 grams of water decompose to give:
a)
4g oxygen and 16g hydrogen
b)
2g hydrogen and 1g oxygen
c)
8g oxygen and 1g hydrogen
d)
none
| | Imk Pathshala answered |
The decomposition of water (H₂O) into its constituent gases yields 1 gram of hydrogen (H₂) and 8 grams of oxygen (O₂) from 9 grams of water, which aligns with the law of conservation of mass.
A student heats 25g of reactant ‘A’ with 50g of reactant ‘B’. He obtains 50g of product ‘C’ and recovers 25 g of unreacted ‘B’. Which of the following law is confirmed in the following reaction?- a)Law of constant proportion
- b)Law of conservation of mass
- c)Law of conservation of mass and Law of constant proportion
- d)Law of multiple proportion
Correct answer is option 'C'. Can you explain this answer?
A student heats 25g of reactant ‘A’ with 50g of reactant ‘B’. He obtains 50g of product ‘C’ and recovers 25 g of unreacted ‘B’. Which of the following law is confirmed in the following reaction?
a)
Law of constant proportion
b)
Law of conservation of mass
c)
Law of conservation of mass and Law of constant proportion
d)
Law of multiple proportion
| | Arvind Singh answered |
Two laws are followed in this question.
First law is Law of definite proportion as follows:
Here 25 g of reactant A reacts with 50 g of reactant B to produce 50 g of product C. That means 25 g of A consumes only 25 g of B. The ratio is 1:1. Even if there would have been say 75 g B is present, still only 25 g of B will react with 25 g of A. Or if 10 g of B is present then only 10 g of A will react and remaining 15 g of A will remain unreacted.
Second law is Law of conservation of mass as follows :
There is 25 g of A and 50 g of B. That means total 75 g of reactant is present. On product side 50 g of C and 25 g of unreacted B is present. That means total 75 g of product is present. Hence, the correct option will be " Law of conservation of mass and Law of constant proportion ".
The balancing of chemical equation is based upon:- a)Law of conservation of mass
- b)Law of multiple proportions
- c)Law of definite proportion
- d)Law of combining volumes
Correct answer is option 'A'. Can you explain this answer?
The balancing of chemical equation is based upon:
a)
Law of conservation of mass
b)
Law of multiple proportions
c)
Law of definite proportion
d)
Law of combining volumes
 | Nikhil Mehra answered |
A chemical equation consists of reactants, products and an arrow showing the direction of reaction. The equation in which number of atoms of all the molecules is equal on both sides of the equation is known as balanced chemical equation. Law of conservation of mass governs the balancing of a chemical equation.
If all the reactants in a chemical reaction are completely used, which of the following statements accurately describes the relationship between the reactants and the products?- a)The reactants must contain more complex molecules than the products do.
- b)The products must have different physical state than the reactants.
- c)The total mass of the reactants must equal the total mass of the products.
- d)The density of the reactants must equal the density of the products.
Correct answer is option 'C'. Can you explain this answer?
If all the reactants in a chemical reaction are completely used, which of the following statements accurately describes the relationship between the reactants and the products?
a)
The reactants must contain more complex molecules than the products do.
b)
The products must have different physical state than the reactants.
c)
The total mass of the reactants must equal the total mass of the products.
d)
The density of the reactants must equal the density of the products.
 | Gaurav Kumar answered |
According to the Law of Conservation of mass, the total mass of the Reactants must equal the total mass of the products.
Which of the following is not a postulate of Dalton’s atomic theory?- a)The number of atoms in a given compound is fixed.
- b)Atoms of the same elements cannot combine in more than one ratio to form more than one compound.
- c)Atoms can neither be created nor destroyed.
- d)Atoms cannot be divided.
Correct answer is option 'B'. Can you explain this answer?
Which of the following is not a postulate of Dalton’s atomic theory?
a)
The number of atoms in a given compound is fixed.
b)
Atoms of the same elements cannot combine in more than one ratio to form more than one compound.
c)
Atoms can neither be created nor destroyed.
d)
Atoms cannot be divided.
| | Nishi Kumari answered |
B is the correct answer
Match the following with correct response. 
- a)1-A, 2-C, 3-B, 4-D
- b)1-D, 2-A, 3-C, 4-B
- c)1-B, 2-D, 3-A, 4-C
- d)1-C, 2-B, 3-D, 4-A
Correct answer is option 'B'. Can you explain this answer?
Match the following with correct response.
a)
1-A, 2-C, 3-B, 4-D
b)
1-D, 2-A, 3-C, 4-B
c)
1-B, 2-D, 3-A, 4-C
d)
1-C, 2-B, 3-D, 4-A
 | EduRev Class 9 answered |
1 u (atomic mass unit) or 1 amu is defined as 1/12th of the mass of a carbon-12 atom.
Which of the following statements is true about the law of conservation of mass?- a)In a chemical reaction, efforts should be made to preserve rare elements without changing them.
- b)In a chemical reaction, the final mass of the products is always greater than the starting mass of the reactants.
- c)In a chemical reaction, matter is not created or destroyed, but is conserved.
- d)Matter can be created and destroyed but does not change forms.
Correct answer is option 'C'. Can you explain this answer?
Which of the following statements is true about the law of conservation of mass?
a)
In a chemical reaction, efforts should be made to preserve rare elements without changing them.
b)
In a chemical reaction, the final mass of the products is always greater than the starting mass of the reactants.
c)
In a chemical reaction, matter is not created or destroyed, but is conserved.
d)
Matter can be created and destroyed but does not change forms.
| | Himangshu Das answered |
Law of conservation of mass states that in a chemical reaction, matter is neither created nor destroyed as it is always conserved.
Hence the option 'c' is correct.
Hence the option 'c' is correct.
Which of the following statement is not in accordance with Dalton’s atomic theory?- a)All matter is made up of very tiny particles called atoms.
- b)Atoms can be divided into proton, neutron and electrons.
- c)Atoms of given element are identical in mass and chemical properties.
- d)Atoms combine in the ratio of small whole numbers to form compounds.
Correct answer is option 'B'. Can you explain this answer?
Which of the following statement is not in accordance with Dalton’s atomic theory?
a)
All matter is made up of very tiny particles called atoms.
b)
Atoms can be divided into proton, neutron and electrons.
c)
Atoms of given element are identical in mass and chemical properties.
d)
Atoms combine in the ratio of small whole numbers to form compounds.
| | Ananya Das answered |
Dalton’s Atomic Theory was given by John Dalton.
According to this theory: -
(a) Matter is made up of invisible particles known as atoms.
(b) The properties of all the atoms of a given element are the same including mass.
(c) Atoms of different elements combine in fixed ratios to form compounds.
(d) Atoms are neither created nor destroyed.
(e) The formation of new products results from the rearrangements of existing atoms.
(f) Atoms of an element are identical in mass, size and properties.
According to this theory: -
(a) Matter is made up of invisible particles known as atoms.
(b) The properties of all the atoms of a given element are the same including mass.
(c) Atoms of different elements combine in fixed ratios to form compounds.
(d) Atoms are neither created nor destroyed.
(e) The formation of new products results from the rearrangements of existing atoms.
(f) Atoms of an element are identical in mass, size and properties.
Match the following with correct response. 
- a)1-D, 2-A, 3-C, 4-B
- b)1-C, 2-B, 3-D, 4-A
- c)1-A, 2-C, 3-B, 4-D
- d)1-B, 2-D, 3-A, 4-C
Correct answer is option 'D'. Can you explain this answer?
Match the following with correct response.
a)
1-D, 2-A, 3-C, 4-B
b)
1-C, 2-B, 3-D, 4-A
c)
1-A, 2-C, 3-B, 4-D
d)
1-B, 2-D, 3-A, 4-C
 | Nk Classes answered |
The Law of Definite Proportions states that a compound always contains the same elements in certain fixed proportions by mass, regardless of its source or how it was prepared.
Match the following with correct response. 
- a)1-D, 2-A, 3-C, 4-B
- b)1-A, 2-C, 3-B, 4-D
- c)1-B, 2-D, 3-A, 4-C
- d)1-C, 2-B, 3-D, 4-A
Correct answer is option 'B'. Can you explain this answer?
Match the following with correct response.
a)
1-D, 2-A, 3-C, 4-B
b)
1-A, 2-C, 3-B, 4-D
c)
1-B, 2-D, 3-A, 4-C
d)
1-C, 2-B, 3-D, 4-A
| | Imk Pathshala answered |
Molecular mass is the sum of the atomic masses of all atoms in a molecule, compared to the mass of a carbon-12 atom.
Law of conservation of mass can be derived from which postulate of Dalton’s atomic theory?- a)Atoms of a given element have same mass and chemical properties.
- b)Matter is made of tiny particles.
- c)Atom can neither be created nor destroyed.
- d)The relative number and kind of atoms are constant in a given compound.
Correct answer is option 'C'. Can you explain this answer?
Law of conservation of mass can be derived from which postulate of Dalton’s atomic theory?
a)
Atoms of a given element have same mass and chemical properties.
b)
Matter is made of tiny particles.
c)
Atom can neither be created nor destroyed.
d)
The relative number and kind of atoms are constant in a given compound.
 | Ankit Saha answered |
According to the law of conservation of mass, mass can neither be created nor destroyed in a chemical reaction.
Which is not true about H2SO4?
A. It is composed of 2 Hydrogen, 1 Sulpher and 4 Oxygen atoms
B. It relative molecular mass is 98
C. It is composed of one molecule of H2 One atom S and two molecules O2
D. Its relative molecular mass is 108 - a)(c) and (d) are incorrect
- b)Only (d) is incorrect
- c)(a), (b) and (c) are incorrect
- d)All of these
Correct answer is option 'B'. Can you explain this answer?
Which is not true about H2SO4?
A. It is composed of 2 Hydrogen, 1 Sulpher and 4 Oxygen atoms
B. It relative molecular mass is 98
C. It is composed of one molecule of H2 One atom S and two molecules O2
D. Its relative molecular mass is 108
A. It is composed of 2 Hydrogen, 1 Sulpher and 4 Oxygen atoms
B. It relative molecular mass is 98
C. It is composed of one molecule of H2 One atom S and two molecules O2
D. Its relative molecular mass is 108
a)
(c) and (d) are incorrect
b)
Only (d) is incorrect
c)
(a), (b) and (c) are incorrect
d)
All of these
 | For Civil answered |
1
An atom has atomic number 11. The number of protons are ________.- a)11
- b)12
- c)23
- d)44
Correct answer is option 'A'. Can you explain this answer?
An atom has atomic number 11. The number of protons are ________.
a)
11
b)
12
c)
23
d)
44
| | Imk Pathshala answered |
- The atomic number of an atom is the number of protons in its nucleus.
- An atom with an atomic number of 11 has 11 protons.
- The correct answer is A: 11.
- An atom with an atomic number of 11 has 11 protons.
- The correct answer is A: 11.
A sample of CaCO3 conatins 3.01×1023 ions of Ca2+ and (CO3)2-.The mass of the sample is- a)100g
- b)5g
- c)200g
- d)50g
Correct answer is option 'D'. Can you explain this answer?
A sample of CaCO3 conatins 3.01×1023 ions of Ca2+ and (CO3)2-.The mass of the sample is
a)
100g
b)
5g
c)
200g
d)
50g
 | Maheshwar Choudhary answered |
The mass of one mole of CaCO3 is equal to 100 g. one mole of is equal to 6.022 × 1023ions. Therefore, mass of 3.01×1023 ions = 50 g
What is the mass of 0.2 mole of lead nitrate? (N=14, O=16, Pb=207)- a)33.1 g
- b)3.31 g
- c)66.2 g
- d)6.62 g
Correct answer is option 'C'. Can you explain this answer?
What is the mass of 0.2 mole of lead nitrate? (N=14, O=16, Pb=207)
a)
33.1 g
b)
3.31 g
c)
66.2 g
d)
6.62 g
 | Shilpa Choudhury answered |
Gram Molecular weight of Pb(NO3)2
= 207 + (2 × 14) + 2 (16 × 3)
= 207 + 28 + 96
= 331
1 mole of Pb(NO3)2 is 331g
Therefore 0.2 mole of Pb(NO3)2 is 331 × 0.2
= 66.2 g
How many litres of ammonia are present in 3.4 kg of it? (N = 14, H = 1)- a)22.4 litres
- b)44.8 litres
- c)4480 litres
- d)2240 litres
Correct answer is option 'C'. Can you explain this answer?
How many litres of ammonia are present in 3.4 kg of it? (N = 14, H = 1)
a)
22.4 litres
b)
44.8 litres
c)
4480 litres
d)
2240 litres
| | Shilpa Choudhury answered |
Gram molecular weight of NH3 = 14 + (1 × 3) = 17 g
17 g of NH3= 22.4 litres
∴ 3.4 × 103g of NH = 22.4/17 × 3.4 × 103
= 76160/17 = 4480 litres
State whether the following statement is True or False:Atoms of a given element are different in mass and chemical properties (except isotopes).- a)True
- b)False
Correct answer is option 'B'. Can you explain this answer?
State whether the following statement is True or False:
Atoms of a given element are different in mass and chemical properties (except isotopes).
a)
True
b)
False
| | EduRev Class 9 answered |
- Atoms of a given element are actually identical in mass and chemical properties. This means that all atoms of the same element have the same mass and behave in the same way chemically. It's like having a bunch of identical Lego blocks that are all the same size and shape. So, the statement is False because atoms of the same element are not different, but they are the same.
The atoms of which of the following pair of elements are most likely to exist in free state?- a)Hydrogen and helium
- b)Helium and neon
- c)Argon and carbon
- d)Neon and nitrogen
Correct answer is option 'B'. Can you explain this answer?
The atoms of which of the following pair of elements are most likely to exist in free state?
a)
Hydrogen and helium
b)
Helium and neon
c)
Argon and carbon
d)
Neon and nitrogen
 | Ridhi Kapoor answered |
Understanding Free State of Atoms
Atoms exist in a free state when they are not bonded to other atoms. This typically occurs with noble gases due to their stable electron configurations.
The Noble Gases
- Noble Gases: Helium (He) and Neon (Ne) belong to Group 18 of the periodic table, known as the noble gases.
- Stability: These elements have complete valence electron shells. Helium has 2 electrons, while Neon has 8. This stability makes them less likely to react with other elements.
Why Helium and Neon Exist in Free State
- Inert Nature: Both helium and neon are chemically inert, meaning they don't readily form compounds with other elements.
- Occurrence: In nature, they are found in their elemental form, often in the atmosphere and are used in applications like balloons and lighting.
Other Elements in the Options
- Hydrogen and Helium: Hydrogen (H) can bond with other elements, while helium is stable.
- Argon and Carbon: Argon (Ar) is inert like the noble gases, but carbon (C) readily forms various compounds.
- Neon and Nitrogen: While neon is inert, nitrogen (N) is very reactive and forms numerous compounds.
Conclusion
The correct answer is option 'B' (Helium and Neon) because both are noble gases that exist in a free state due to their stable electronic configurations and inert nature.
Atoms exist in a free state when they are not bonded to other atoms. This typically occurs with noble gases due to their stable electron configurations.
The Noble Gases
- Noble Gases: Helium (He) and Neon (Ne) belong to Group 18 of the periodic table, known as the noble gases.
- Stability: These elements have complete valence electron shells. Helium has 2 electrons, while Neon has 8. This stability makes them less likely to react with other elements.
Why Helium and Neon Exist in Free State
- Inert Nature: Both helium and neon are chemically inert, meaning they don't readily form compounds with other elements.
- Occurrence: In nature, they are found in their elemental form, often in the atmosphere and are used in applications like balloons and lighting.
Other Elements in the Options
- Hydrogen and Helium: Hydrogen (H) can bond with other elements, while helium is stable.
- Argon and Carbon: Argon (Ar) is inert like the noble gases, but carbon (C) readily forms various compounds.
- Neon and Nitrogen: While neon is inert, nitrogen (N) is very reactive and forms numerous compounds.
Conclusion
The correct answer is option 'B' (Helium and Neon) because both are noble gases that exist in a free state due to their stable electronic configurations and inert nature.
The atomic number of an element X is 13. What will be the number of electrons in its ion X3+?- a)11
- b)16
- c)15
- d)10
Correct answer is option 'D'. Can you explain this answer?
The atomic number of an element X is 13. What will be the number of electrons in its ion X3+?
a)
11
b)
16
c)
15
d)
10
 | Sarika Singh answered |
Atomic Number and Number of Electrons
The atomic number of an element represents the number of protons in the nucleus of an atom of that element. Since atoms are electrically neutral, the number of protons is equal to the number of electrons orbiting the nucleus.
Ion Formation
An ion is formed when an atom gains or loses electrons. If an atom gains electrons, it becomes negatively charged and is called an anion. If an atom loses electrons, it becomes positively charged and is called a cation.
Determining the Number of Electrons in an Ion
To determine the number of electrons in an ion, we need to know the charge of the ion. The charge of an ion is indicated by a superscript after the element symbol. For example, X3 indicates that the ion has a charge of +3.
Calculation
In this case, the element X has an atomic number of 13. This means it has 13 protons and 13 electrons in its neutral state. The ion X3 has a charge of +3, indicating that it has lost 3 electrons.
To find the number of electrons in the ion X3, we subtract the charge of the ion from the number of electrons in the neutral atom.
Number of electrons in ion X3 = Number of electrons in neutral atom - Charge of ion
Number of electrons in ion X3 = 13 electrons - 3 electrons
Number of electrons in ion X3 = 10 electrons
Therefore, the correct answer is option D) 10. The ion X3 has 10 electrons.
The atomic number of an element represents the number of protons in the nucleus of an atom of that element. Since atoms are electrically neutral, the number of protons is equal to the number of electrons orbiting the nucleus.
Ion Formation
An ion is formed when an atom gains or loses electrons. If an atom gains electrons, it becomes negatively charged and is called an anion. If an atom loses electrons, it becomes positively charged and is called a cation.
Determining the Number of Electrons in an Ion
To determine the number of electrons in an ion, we need to know the charge of the ion. The charge of an ion is indicated by a superscript after the element symbol. For example, X3 indicates that the ion has a charge of +3.
Calculation
In this case, the element X has an atomic number of 13. This means it has 13 protons and 13 electrons in its neutral state. The ion X3 has a charge of +3, indicating that it has lost 3 electrons.
To find the number of electrons in the ion X3, we subtract the charge of the ion from the number of electrons in the neutral atom.
Number of electrons in ion X3 = Number of electrons in neutral atom - Charge of ion
Number of electrons in ion X3 = 13 electrons - 3 electrons
Number of electrons in ion X3 = 10 electrons
Therefore, the correct answer is option D) 10. The ion X3 has 10 electrons.
What does the Law of Constant Proportions tell us about chemical compounds?- a)They contain different elements in different proportions
- b)They always have the same elements in the same proportion by mass
- c)They change their elements when prepared differently
- d)They have elements that vary in mass randomly
Correct answer is option 'B'. Can you explain this answer?
What does the Law of Constant Proportions tell us about chemical compounds?
a)
They contain different elements in different proportions
b)
They always have the same elements in the same proportion by mass
c)
They change their elements when prepared differently
d)
They have elements that vary in mass randomly
 | Let's Tute answered |
- The Law of Constant Proportions teaches us that chemical compounds, like water or ammonia, always keep the same elements in the same proportion by weight no matter where they come from or how they are made. This means that in water, for example, there will always be a fixed ratio of hydrogen to oxygen, and in ammonia, nitrogen to hydrogen will always be in a set proportion.
Which of the following is correct for the ‘Law of Conservation of Mass’?- a)Mass can neither be created nor destroyed.
- b)The rate of reaction is directly proportional to the active mass of the reactants.
- c)Mass can either be created or destroyed in a chemical reaction.
- d)The elements are always present in a constant proportion in a chemical substance
Correct answer is option 'A'. Can you explain this answer?
Which of the following is correct for the ‘Law of Conservation of Mass’?
a)
Mass can neither be created nor destroyed.
b)
The rate of reaction is directly proportional to the active mass of the reactants.
c)
Mass can either be created or destroyed in a chemical reaction.
d)
The elements are always present in a constant proportion in a chemical substance
| | Himaja Ammu answered |
Law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction....
It was proposed by Antoine lavoisier but experimentally proved by landolt
It was proposed by Antoine lavoisier but experimentally proved by landolt
The atomic theory of matter was proposed by- a)Lavoisier
- b)Proust
- c)John Dalton
- d)John Kennedy
Correct answer is option 'C'. Can you explain this answer?
The atomic theory of matter was proposed by
a)
Lavoisier
b)
Proust
c)
John Dalton
d)
John Kennedy
| | Shilpa Choudhury answered |
The atomic theory of matter was proposed by John Dalton.
John Dalton (1766-1844) developed the first useful atomic theory of matter.
In water, hydrogen and oxygen are present in the ratio of- a)1 : 2
- b)1 : 8
- c)2 : 12
- d)2 : 3
Correct answer is option 'B'. Can you explain this answer?
In water, hydrogen and oxygen are present in the ratio of
a)
1 : 2
b)
1 : 8
c)
2 : 12
d)
2 : 3
 | Nikhil Malik answered |
Understanding the Composition of Water
Water is a chemical compound composed of hydrogen and oxygen. Its molecular formula is H2O, indicating that each molecule of water consists of two hydrogen atoms and one oxygen atom.
Ratio of Elements in Water
- Hydrogen Atoms: 2 (from H2)
- Oxygen Atoms: 1 (from O)
To find the ratio of the masses of hydrogen to oxygen in water, we need to consider the atomic masses of these elements:
- Atomic Mass of Hydrogen: Approximately 1 g/mol
- Atomic Mass of Oxygen: Approximately 16 g/mol
Calculating the Mass Ratio
- Mass of Hydrogen in H2O:
- 2 Hydrogen atoms x 1 g/mol = 2 g
- Mass of Oxygen in H2O:
- 1 Oxygen atom x 16 g/mol = 16 g
Now, we can express the mass ratio of hydrogen to oxygen:
- Mass Ratio: 2 g (H) : 16 g (O)
This can be simplified to:
- Simplified Ratio: 1 : 8
Conclusion
Therefore, in water, the ratio of hydrogen to oxygen by mass is indeed 1:8. The correct answer to the question is option 'B'.
Water is a chemical compound composed of hydrogen and oxygen. Its molecular formula is H2O, indicating that each molecule of water consists of two hydrogen atoms and one oxygen atom.
Ratio of Elements in Water
- Hydrogen Atoms: 2 (from H2)
- Oxygen Atoms: 1 (from O)
To find the ratio of the masses of hydrogen to oxygen in water, we need to consider the atomic masses of these elements:
- Atomic Mass of Hydrogen: Approximately 1 g/mol
- Atomic Mass of Oxygen: Approximately 16 g/mol
Calculating the Mass Ratio
- Mass of Hydrogen in H2O:
- 2 Hydrogen atoms x 1 g/mol = 2 g
- Mass of Oxygen in H2O:
- 1 Oxygen atom x 16 g/mol = 16 g
Now, we can express the mass ratio of hydrogen to oxygen:
- Mass Ratio: 2 g (H) : 16 g (O)
This can be simplified to:
- Simplified Ratio: 1 : 8
Conclusion
Therefore, in water, the ratio of hydrogen to oxygen by mass is indeed 1:8. The correct answer to the question is option 'B'.
The anion of an element has- a)Less electrons than the normal atom
- b)More electrons than the normal atom
- c)More protons than the normal atom
- d)Same number of electrons as normal atom
Correct answer is option 'B'. Can you explain this answer?
The anion of an element has
a)
Less electrons than the normal atom
b)
More electrons than the normal atom
c)
More protons than the normal atom
d)
Same number of electrons as normal atom
| | Shilpa Choudhury answered |
The anion of an element has a single negative charge. The VI A elements gain two electrons to form anions with a 2- charge.
For example, consider sodium cations (Na+) and Chloride anions (Cl−). Sodium has a positive 1 charge and chloride has a negative 1 charge.
The anion of an element has more electrons than the normal atom because it is formed by gaining electrons.
According to Law of conservation of mass, mass of reactants wil be equal to the mass of:- a)Catalysts
- b)Products
- c)Apparatus used for reaction
- d)Gases evolved
Correct answer is option 'B'. Can you explain this answer?
According to Law of conservation of mass, mass of reactants wil be equal to the mass of:
a)
Catalysts
b)
Products
c)
Apparatus used for reaction
d)
Gases evolved
| | Himaja Ammu answered |
Law of conversation of mass:in a chemical reaction mass of reactants must be equal to the mass of products because atoms r neither created nor destroyed in a chemical reaction. This was proposed by Antoine lavoisier but experimentally proved by landolt.
Which postulates of Dalton’s atomic theory gives laws of conservation of mass- a)Atom can neither be created nor be destroyed
- b)Atoms of same elements are similar
- c)Atoms of different elements are different
- d)Atom combine in fixed ratio to form compound
Correct answer is option 'A'. Can you explain this answer?
Which postulates of Dalton’s atomic theory gives laws of conservation of mass
a)
Atom can neither be created nor be destroyed
b)
Atoms of same elements are similar
c)
Atoms of different elements are different
d)
Atom combine in fixed ratio to form compound
| | Shilpa Choudhury answered |
The postulate of Dalton’s atomic theory resulting from the law of conservation of mass is ‘The relative number and kinds of atoms are constant in a given compound. Atoms cannot be created nor destroyed in a chemical reaction’.
The smallest particle of a substance that is capable of independent existence is- a)Electron
- b)Proton
- c)Atom
- d)Molecule
Correct answer is option 'D'. Can you explain this answer?
The smallest particle of a substance that is capable of independent existence is
a)
Electron
b)
Proton
c)
Atom
d)
Molecule
| | Anaya Desai answered |
The Smallest Particle with Independent Existence
In the realm of chemistry and physics, understanding the fundamental particles that compose matter is crucial. Among the options given, the correct answer is "Molecule." Let's delve deeper into why this is the case.
Understanding Particles
- Electron:
- A subatomic particle with a negative charge.
- Cannot exist independently as a substance, as it is a component of atoms.
- Proton:
- A positively charged subatomic particle found in the nucleus of an atom.
- Like electrons, protons are not standalone entities; they are part of atomic structure.
- Atom:
- The basic unit of a chemical element.
- Atoms can exist independently, but they are comprised of smaller particles (protons, neutrons, and electrons).
Why Molecule is the Correct Answer
- Definition of a Molecule:
- A molecule is formed when two or more atoms bond together.
- It represents the smallest particle of a substance that retains the physical and chemical properties of that substance.
- Independent Existence:
- Molecules can exist independently; they can be gases, liquids, or solids.
- For example, a water molecule (H2O) can exist independently as a drop of water.
Conclusion
In essence, while electrons and protons are fundamental components of atoms, they cannot exist independently as substances. Atoms can exist independently but do not represent the smallest unit that retains substance properties. Molecules, being combinations of atoms, hold the ability to exist independently, making them the smallest particles of substances capable of such existence. Thus, option 'D' is indeed the correct answer.
In the realm of chemistry and physics, understanding the fundamental particles that compose matter is crucial. Among the options given, the correct answer is "Molecule." Let's delve deeper into why this is the case.
Understanding Particles
- Electron:
- A subatomic particle with a negative charge.
- Cannot exist independently as a substance, as it is a component of atoms.
- Proton:
- A positively charged subatomic particle found in the nucleus of an atom.
- Like electrons, protons are not standalone entities; they are part of atomic structure.
- Atom:
- The basic unit of a chemical element.
- Atoms can exist independently, but they are comprised of smaller particles (protons, neutrons, and electrons).
Why Molecule is the Correct Answer
- Definition of a Molecule:
- A molecule is formed when two or more atoms bond together.
- It represents the smallest particle of a substance that retains the physical and chemical properties of that substance.
- Independent Existence:
- Molecules can exist independently; they can be gases, liquids, or solids.
- For example, a water molecule (H2O) can exist independently as a drop of water.
Conclusion
In essence, while electrons and protons are fundamental components of atoms, they cannot exist independently as substances. Atoms can exist independently but do not represent the smallest unit that retains substance properties. Molecules, being combinations of atoms, hold the ability to exist independently, making them the smallest particles of substances capable of such existence. Thus, option 'D' is indeed the correct answer.
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