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Test : Atoms And Molecules- 2 UPSC Sci & Tech MCQs solutions - Free


MCQ Practice Test & Solutions: Test : Atoms And Molecules- 2 (20 Questions)

You can prepare effectively for UPSC Science & Technology for UPSC CSE with this dedicated MCQ Practice Test (available with solutions) on the important topic of "Test : Atoms And Molecules- 2". These 20 questions have been designed by the experts with the latest curriculum of UPSC 2026, to help you master the concept.

Test Highlights:

  • - Format: Multiple Choice Questions (MCQ)
  • - Duration: 20 minutes
  • - Number of Questions: 20

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Test : Atoms And Molecules- 2 - Question 1
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Which one of the following phrases would be incorrect to use?

Detailed Solution: Question 1

 it  will be incorrect to say that  an  atom of  a compound   because, 
Every combination of atoms is a molecule. A compound is a molecule made of atoms  from different elements. All compounds are molecules , but not all molecules are compounds.

Test : Atoms And Molecules- 2 - Question 2
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Which of the following illustrates the law of conservation of mass?

Detailed Solution: Question 2

Option 2 illustrates the law of conservation of mass.

The law of conservation of mass states that in a chemical reaction, the total mass of the reactants is equal to the total mass of the products. This means that matter is neither created nor destroyed in a chemical reaction.

In option 2, 12 g of CO reacts with 32 g of O2 to form 44 g of CO2. The total mass of the reactants (12 g + 32 g = 44 g) is equal to the total mass of the product (44 g). This illustrates the law of conservation of mass.

Option 1 is an example of the law of definite proportions, which states that a given compound always contains the same elements in the same proportion by mass.

Option 3 is not a valid example of the law of conservation of mass, as heating carbon in a vacuum can lead to the release of gases such as carbon dioxide, carbon monoxide, and carbon suboxide, which can escape and change the mass of the system.

Option 4 is an example of a physical change, where the state of matter of a substance changes, but the mass of the substance remains the same. It does not illustrate the law of conservation of mass.

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Test : Atoms And Molecules- 2 - Question 3
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The law of constant proportion was proposed by

Detailed Solution: Question 3

In 1806, Proust summarized his observations in what is now called Proust's Law. It stated that chemical compounds are formed of constant and defined ratios of elements, as determined by mass. For example, carbon dioxide is composed of one carbon atom and two oxygen atoms.

Test : Atoms And Molecules- 2 - Question 4
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A compound contains 8% sulphur by mass. The minimum molecular weight of the compound is:

Detailed Solution: Question 4

The compound Sulphur = 8%
Therefore, 8g of S is present in 100g.
(Least molecular mass means that at least one atom of Sulphur should be present in a molecule.)
Therefore, 32g of S is peasant in 100/8 x 32 = 400

Test : Atoms And Molecules- 2 - Question 5
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The mass of one atom of carbon-12 is

Detailed Solution: Question 5

Mass of one atom = Avogadro′s numberMass of one mole of atom​=12/6.02×1023

Mass of one carbon atom = 1.994×10−23g

Test : Atoms And Molecules- 2 - Question 6
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Identify the correct one from the following statements. 

Detailed Solution: Question 6

option ( c) The mixture has properties similar to its compound is the correct answer. 

Explanation:- 

This is because in a mixture, the constituent particles are not mixed chemically.
They are mixed physically and can be separated fairly easily by physical Methods.
Thus they show the properties of components.
Example can be alloys.

Test : Atoms And Molecules- 2 - Question 7
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The atom is indivisible, was proposed by

Detailed Solution: Question 7

Explanation:
1. Dalton's Atomic Theory:
- The proposal that the atom is indivisible was put forth by John Dalton.
- Dalton's atomic theory, published in the early 19th century, laid the foundation for modern atomic theory.
- According to Dalton, atoms are indivisible and indestructible particles.
- He believed that all elements are composed of atoms and that chemical reactions involve the rearrangement of atoms.
2. Einstein's Contribution:
- While Albert Einstein made significant contributions to the field of physics, he did not propose the idea that the atom is indivisible.
- Einstein's most famous work is the theory of relativity, which revolutionized our understanding of space, time, and gravity.
3. Lavoisier and Proust:
- Antoine Lavoisier and Joseph Proust were influential chemists, but they did not propose the indivisibility of the atom.
- Lavoisier is known as the father of modern chemistry for his contributions to the understanding of chemical reactions and the discovery of oxygen's role in combustion.
- Proust is best known for the law of definite proportions, which states that a chemical compound always contains the same elements in fixed proportions by weight.
Conclusion:
- The correct answer is C: Dalton, who proposed that the atom is indivisible, as part of his atomic theory.

Test : Atoms And Molecules- 2 - Question 8
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18 g of water is electrolysed. The weight of oxygen formed will be 

Detailed Solution: Question 8

Problem:
18 g of water is electrolysed. The weight of oxygen formed will be?

To determine the weight of oxygen formed during electrolysis of water, we need to use the concept of stoichiometry and the molar mass of water.
Stoichiometry:
The balanced chemical equation for the electrolysis of water is:
2H2O → 2H2 + O2
From the equation, we can see that for every 2 moles of water electrolyzed, 1 mole of oxygen gas is formed.
Molar Mass:
The molar mass of water (H2O) is calculated as follows:
Molar mass of H2O = (2 * atomic mass of hydrogen) + atomic mass of oxygen
= (2 * 1.008 g/mol) + 16.00 g/mol
= 18.016 g/mol
Calculations:
1 mole of water weighs 18.016 g.
Therefore, 18 g of water is equal to (18 g / 18.016 g/mol) = 0.9998 moles of water.
Since the mole ratio between water and oxygen is 2:1, the moles of oxygen formed will be half of the moles of water electrolyzed.
Moles of oxygen = (0.9998 moles of water) / 2
= 0.4999 moles
Finally, we can calculate the weight of oxygen using its molar mass:
Weight of oxygen = (moles of oxygen) * (molar mass of oxygen)
= 0.4999 moles * 32.00 g/mol
= 15.9968 g
Conclusion:
The weight of oxygen formed during the electrolysis of 18 g of water is approximately 16 g. Therefore, the correct answer is option A: 16 g.

Test : Atoms And Molecules- 2 - Question 9
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Modern atomic symbols are based on the method proposed by

Detailed Solution: Question 9

Modern atomic symbols are based on the method proposed by Berzelius

Explanation:



  • Berzelius: Jöns Jacob Berzelius was a Swedish chemist who proposed a method for representing elements using symbols.

  • Atomic Symbols: Atomic symbols are abbreviated representations of chemical elements. They are used to represent elements in chemical equations and discussions.

  • Berzelius' Method: Berzelius proposed a method of using one or two letters to represent elements. For example, the symbol "H" represents hydrogen, "O" represents oxygen, and "Na" represents sodium.

  • Importance: Berzelius' method of atomic symbols provided a more concise and standardized way to represent elements, making it easier for scientists to communicate and understand chemical reactions and properties.

  • Continued Use: Berzelius' method of atomic symbols is still used today. The symbols for elements on the periodic table are based on his system.


Therefore, the correct answer is B: Berzelius.

Test : Atoms And Molecules- 2 - Question 10
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The balancing of chemical equation is based on 

Detailed Solution: Question 10

Explanation:
The balancing of chemical equations is based on the Law of Conservation of Mass. This law states that mass is neither created nor destroyed during a chemical reaction. In other words, the total mass of the reactants is equal to the total mass of the products.
To balance a chemical equation, one must ensure that there is the same number of atoms of each element on both sides of the equation. This can be achieved by adjusting the coefficients in front of the chemical formulas.
Here is a detailed explanation of how the Law of Conservation of Mass is applied in balancing chemical equations:
1. Identify the reactants and products: Determine the chemical formulas of the reactants and products involved in the reaction.
2. Count the atoms: Count the number of atoms of each element present in the reactants and products.
3. Balance the elements: Adjust the coefficients in front of the chemical formulas to ensure that the same number of atoms of each element is present on both sides of the equation.
4. Check the balance: Verify that the number of atoms of each element is equal on both sides of the equation.
5. Adjust coefficients: If the equation is not balanced, continue adjusting the coefficients until the equation is balanced.
By following these steps and applying the Law of Conservation of Mass, one can successfully balance a chemical equation.

Test : Atoms And Molecules- 2 - Question 11
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Which of the following is the chemical symbol for nitrogen gas?

Detailed Solution: Question 11

The chemical formula of Nitrogen is N but Nitrogen exists in the molecule of two ions hence the chemical symbol of Nitrogen gas is written as N2.

Test : Atoms And Molecules- 2 - Question 12
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Which of the following is correct statement ?

Detailed Solution: Question 12

Correct Statement:
The correct statement is A:
- Na2S is Sodium sulphide.
- Na2S03 is Sodium sulphite.
- Na2S04 is Sodium sulphate.

Test : Atoms And Molecules- 2 - Question 13
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Latin name for iron is

Detailed Solution: Question 13

Latin name for iron is:
- The Latin name for iron is ferrum.
- The options given are:
A: ferrous
B: ferrum
C: ferric
D: none of these
- To determine the correct answer, we need to know the Latin name for iron.
- The Latin name for iron is ferrum.
- Therefore, the correct answer is option b.
- Option a (ferrous) refers to the adjective form of iron, which means containing iron.
- Option c (ferric) refers to the form of iron with a valence of +3.
- Option d (none of these) is incorrect as the Latin name for iron is ferrum.
- It is important to note that the Latin name for iron is widely used in scientific and medical contexts.

Test : Atoms And Molecules- 2 - Question 14
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Molecular weight of CuS04. 5H20 is equal to 
[Cu = 63.5 u, S = 32 u, O — 16 u, H = 1 u]

Detailed Solution: Question 14


The molecular weight of CuSO4.5H2O can be calculated by adding up the atomic weights of its constituent elements.
1. Cu (copper) has an atomic weight of 63.5 u.
2. S (sulfur) has an atomic weight of 32 u.
3. O (oxygen) has an atomic weight of 16 u.
4. H (hydrogen) has an atomic weight of 1 u.
To calculate the molecular weight of CuSO4.5H2O, we need to consider the number of atoms of each element in the compound:
1. Cu: There is only one Cu atom in the compound, so its contribution to the molecular weight is 63.5 u.
2. S: There is one S atom in the compound, so its contribution to the molecular weight is 32 u.
3. O: There are four O atoms in the compound, so their total contribution to the molecular weight is 4 * 16 u = 64 u.
4. H: There are ten H atoms in the compound, so their total contribution to the molecular weight is 10 * 1 u = 10 u.
5. Additionally, there is a water molecule (H2O) attached to the CuSO4 molecule. The molecular weight of H2O is 18 u.
Now, let's calculate the molecular weight:
Cu: 1 * 63.5 u = 63.5 u
S: 1 * 32 u = 32 u
O: 4 * 16 u = 64 u
H: 10 * 1 u = 10 u
H2O: 1 * 18 u = 18 u
Total molecular weight = 63.5 u + 32 u + 64 u + 10 u + 18 u = 187.5 u
Therefore, the molecular weight of CuSO4.5H2O is 187.5 u.
The correct answer is not listed among the given options. Please recheck the options or provide the correct answer.

Test : Atoms And Molecules- 2 - Question 15
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Which of the following represents a correct chemical formula?

Detailed Solution: Question 15


To determine the correct chemical formula, we need to analyze each option and identify any errors.
Option A: CaCI
This option is incorrect because it is missing a subscript for the chlorine ion. The correct formula for calcium chloride is CaCl2.
Option B: NaS04
This option is incorrect because it contains an incorrect subscript. The correct formula for sodium sulfate is Na2SO4.
Option C: NaS
This option is incorrect because it does not represent a valid compound. It combines sodium (Na) with sulfur (S), but there is no such compound with this formula.
Option D: NaCl
This option is correct. It represents the chemical formula for sodium chloride, which is a common and well-known compound.
Therefore, the correct chemical formula is option D: NaCl.

Test : Atoms And Molecules- 2 - Question 16
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How many moles of electrons weigh equal to one kilogram? [Mass of 1 e = 9.1 x 10-31 kg]

Detailed Solution: Question 16


To find the number of moles of electrons that weigh equal to one kilogram, we need to use the equation:
moles of electrons = mass of electrons / molar mass of electrons
Given:
Mass of 1 electron = 9.1 x 10-31 kg
To calculate the molar mass of electrons, we need to convert the mass of 1 electron to grams:
Mass of 1 electron = 9.1 x 10-31 kg x 1000 g/kg = 9.1 x 10-28 g
Now, we can calculate the molar mass of electrons by multiplying the mass of 1 electron by Avogadro's number:
Molar mass of electrons = (9.1 x 10-28 g) x (6.022 x 1023 electrons/mole) = 5.49 g/mol
Now, we can calculate the number of moles of electrons that weigh equal to one kilogram:
moles of electrons = (1 kg) / (5.49 g/mol) = 1.82 x 102 mol
Therefore, the number of moles of electrons that weigh equal to one kilogram is 1.82 x 102 mol, which is approximately equal to 182 mol.
Answer: D

Test : Atoms And Molecules- 2 - Question 17
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3.42 g sucrose are dissolved in 18 g of water in a beaker. The number of oxygen atoms in the solution are

Detailed Solution: Question 17

Molar mass of sucrose = 342 g
No. of Oxygen atoms in 3.42g of (C₁₂H₂₂O₁₁) = 11 x NA
Therefore, No. of Oxygen atoms in 342g of (C₁₂H₂₂O₁₁) = 11 x Na x 3.42 / 342
= 0.11 NA
No. of oxygen atoms in 18g of H₂O = 1NA 
Therefore, Total no. of Oxygen atom in 342g of Sucrose and 18g of water 
= 0.11NA +1NA = 1.11NA = 1.11 x 6.02 x 10²³ ⇒ 6.68 * 1023

Test : Atoms And Molecules- 2 - Question 18
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Arrange the following in increasing order of number of molecules. 
I. 0.5 mol of H2 
II. 4.0 g of H2 
III. 18 g of H2O 
IV 2.2 g of CO2 

Detailed Solution: Question 18

option ( b) is the correct✔ answer. 

Explanation:- first we have to calculate, the no. of molecules  and then we will compare them. To calculate the number of molecules, we multiply no. of moles with the Avagadro's number. 

  • 0.5 *( 6.022 * 10^23) 

=  3.11 * 10^ 23

  • 2* ( 6.022 * 10^23) 

=  12.044 * 10^ 23

  • 3.35 * 10^19

  • 0.05 * ( 6.022 * 10^23) 

= 0.3011 * 10^ 23


So, we can see, 4<1<3<2   is the correct✔ answer.

Test : Atoms And Molecules- 2 - Question 19
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Which of the following symbols is incorrect?
(i) Helium (He)
(ii) Aluminium (AL)
(iii) Carbon (c)
(iv) Cobalt (CO)
Select the correct alternative:

Detailed Solution: Question 19

Because , the symbol used for aluminum is Al,  the symbol used for carbon is C,  the symbol used for cobalt is Co.

Test : Atoms And Molecules- 2 - Question 20
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The mass of sodium in 5.85 g of NaCl is 

Detailed Solution: Question 20


To find the mass of sodium in 5.85 g of NaCl, we need to calculate the molar mass of NaCl and then determine the mass of sodium.
1) Calculate the molar mass of NaCl:
- The molar mass of NaCl is the sum of the molar masses of sodium (Na) and chlorine (Cl).
- The atomic mass of sodium (Na) is 22.99 g/mol.
- The atomic mass of chlorine (Cl) is 35.45 g/mol.
- Therefore, the molar mass of NaCl is 22.99 g/mol + 35.45 g/mol = 58.44 g/mol.
2) Determine the mass of sodium:
- Sodium (Na) has a molar mass of 22.99 g/mol.
- In NaCl, the molar ratio of sodium to NaCl is 1:1.
- Therefore, the mass of sodium in 1 mole of NaCl is 22.99 g.
- To find the mass of sodium in 5.85 g of NaCl, we can use the following proportion:
Mass of sodium / Mass of NaCl = 22.99 g / 58.44 g/mol
Mass of sodium = (5.85 g * 22.99 g) / 58.44 g/mol
Mass of sodium = 2.31 g
3) Answer:
- The mass of sodium in 5.85 g of NaCl is 2.31 g.
Final Answer:
The mass of sodium in 5.85 g of NaCl is 2.31 g. (Option A)

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