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CBSE Class 9  >  Class 9 Test  >  Online MCQ Tests  >  Important Questions (1 mark): Atoms and Molecules - Class 9 MCQ

Important Questions (1 mark): Atoms and Molecules - Free MCQ Test


MCQ Practice Test & Solutions: Important Questions (1 mark): Atoms and Molecules (20 Questions)

You can prepare effectively for Class 9 Online MCQ Tests for Class 9 with this dedicated MCQ Practice Test (available with solutions) on the important topic of "Important Questions (1 mark): Atoms and Molecules". These 20 questions have been designed by the experts with the latest curriculum of Class 9 2026, to help you master the concept.

Test Highlights:

  • - Format: Multiple Choice Questions (MCQ)
  • - Duration: 25 minutes
  • - Number of Questions: 20

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Important Questions (1 mark): Atoms and Molecules - Question 1
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The elements present in baking soda are -

Detailed Solution: Question 1

Baking soda, also called sodium bicarbonate, is a common baking ingredient, cleaner, deodorizer and pH regulator. It is commonly sold as a white powder that looks similar to baking powder. Unlike baking powder, which contains acidic ingredients, however, baking soda is a single compound composed of only four elements: sodium, hydrogen, carbon and oxygen.

Important Questions (1 mark): Atoms and Molecules - Question 2
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The first scientist to use of the symbols of elements was-

Detailed Solution: Question 2

John Dalton
John Dalton was the first scientist to use symbols for elements. He was first to use chemical symbols for elements perfectly in his table of elements , which made chemical chemistry easy.

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Important Questions (1 mark): Atoms and Molecules - Question 3
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The overall charge on an ionic compound is equal to -

Detailed Solution: Question 3

The compound made up of ions is known as ionic compound. Since an ionic compound consists of equal number of positive and negative ions, the overall charge of an ionic compound is zero.

Important Questions (1 mark): Atoms and Molecules - Question 4
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The chemical formula of the copper nitrate -

Detailed Solution: Question 4

Copper nitrate, also known as Cupric nitrate and its chemical formula is Cu(NO3)2

Important Questions (1 mark): Atoms and Molecules - Question 5
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The number of carbon atoms in 1g of CaCO3 is-

Detailed Solution: Question 5

First we calculate the number of moles of CaCO3
Molecular weight of CaCO3 = 100g
Therefore, 100g of CaCO3 will have Avogadro number of molecules (6.022x10²³).
so 1g will have
   (6.022x10²³) x 1/100
= 6.022x10²¹
Now one molecule of CaCO3 has 1 carbon atom. So, 6.022x10²¹ molecules will have 6.022x10²¹ atoms of Carbon.
Answer is (b) 6.022x10²¹

Important Questions (1 mark): Atoms and Molecules - Question 6
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The mass of a single atom of carbon is -

Detailed Solution: Question 6

Mass of one atom = Mass of one mole of atom / Avogadro’s no. 
=  12/  6.02 x 10²³
Mass of one carbon atom = 1.994 x 10¯²³

Important Questions (1 mark): Atoms and Molecules - Question 7
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The mass of 1 u is -

Detailed Solution: Question 7

1u = 1/12 Mass of the carbon atom (12c)  
6.022X1023 atoms of carbon = 12 g  
I atom of carbon = 12/6.022x1023 g  
= 1.99x10-23 g  
1u = 1.99 x 10−23 /12 
= 1.66x10-24 g

Important Questions (1 mark): Atoms and Molecules - Question 8
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How many molecules are present in 9g of water -

Detailed Solution: Question 8

No. of molecules in 9g of water:

Molecular mass of water(H2O)= (1x2)+16=18g/mol

1 mole of water=18g of water contains=6.022x10^23 molecules of water

then 9g of water will have= (6.022x10^23/18)x9 = 3.011x10^23 molecules

Important Questions (1 mark): Atoms and Molecules - Question 9
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Important Questions (1 mark): Atoms and Molecules - Question 10
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The formula of sulphuric acid is-

Detailed Solution: Question 10


The formula of sulphuric acid is H2SO4.
Here is a detailed explanation:
1. Introduction:
Sulphuric acid is a strong acid commonly used in various industrial processes. It is a colorless, odorless liquid with the formula H2SO4.
2. Composition:
Sulphuric acid is composed of the following elements:
- 2 hydrogen atoms (H2)
- 1 sulfur atom (S)
- 4 oxygen atoms (O4)
3. Chemical Formula:
The chemical formula of sulphuric acid is H2SO4. This means that each molecule of sulphuric acid contains 2 hydrogen atoms, 1 sulfur atom, and 4 oxygen atoms.
4. Explanation:
To determine the formula of sulphuric acid, we need to consider the valence of each element. Hydrogen has a valence of +1, sulfur has a valence of +6, and oxygen has a valence of -2. By balancing the charges, we can determine that 2 hydrogen atoms are needed to balance the charge of 1 sulfur atom and 4 oxygen atoms. This gives us the formula H2SO4.
Therefore, the correct answer is option B: H2SO4.

Important Questions (1 mark): Atoms and Molecules - Question 11
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Which of the following has largest number of particles?

Detailed Solution: Question 11

The largest number of particles are in (d) 2g of H2
8g of CH4 = 8 / 16 = 0.5 moles = 3.011 × 10²³ atoms 
4.4g of CO2 = 4.4 / 44 = 0.1 moles = 0.6022 × 10²³ atoms
34.2g of C12H22O11 = 34.2 / 342 = 0.1 moles = 0.6022 × 10²³ atoms
2g of H2 = 2 / 2 = 1 moles = 6.022 × 10²³ atoms
Hence, the correct answer is Option D.

Important Questions (1 mark): Atoms and Molecules - Question 12
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Mass of one Avogadro's number of O atom is equal to -

Detailed Solution: Question 12

1 mole of any atom is = 6.022 x 10 ^23 atom ( avogadro's number ) now, there are Avogadro's number of O atom, which will be = 1 mole ie ; we have 1 mole oxygen atom . mole = weight / molecular weight 1 = weight / 16 ( molecular weight of O = 16 a.m.u ) weight = 16 g ( answer )

Important Questions (1 mark): Atoms and Molecules - Question 13
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How many molecules are present in one gram of hydrogen gas?

Detailed Solution: Question 13

The correct option is B.
One gram of hydrogen contains 1 mole of hydrogen as its atomic weight is 1
1 mole =6.023×1023 atoms.

But, hydrogen is a diatomic molecule.
So, its atoms are found in pairs.

Amount of molecule =3.02×1023
 
∴3.02×1023
  molecules are present in one gram of hydrogen.

Important Questions (1 mark): Atoms and Molecules - Question 14
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The correct formula of aluminium sulphate is

Detailed Solution: Question 14

Explanation:

  • The formula for aluminium sulphate is determined by the charges of the ions involved.

  • Aluminium has a charge of +3, while sulphate has a charge of -2.

  • In order to balance the charges, we need two aluminium ions (Al3+) and three sulphate ions (SO42-).

  • Therefore, the correct formula for aluminium sulphate is Al2(SO4)3.


Summary:

The correct formula for aluminium sulphate is Al2(SO4)3.

Important Questions (1 mark): Atoms and Molecules - Question 15
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Which of the following has highest intermolecular forces of attraction -

Detailed Solution: Question 15

As the carbon dioxide is in solid form(dry ice) so it has gained all the properties of solid i.e. now they have highest intermolecular force between them.

Important Questions (1 mark): Atoms and Molecules - Question 16
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Which of the following is not correct regarding gases?

Detailed Solution: Question 16

Gases have strong tendency to diffuse. Gases have high kinetic energy which because of weak intermolecular forces. This makes them move faster which makes their diffusion fast.

Important Questions (1 mark): Atoms and Molecules - Question 17
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The Boiling point of water at normal atmospheric pressure is -

Detailed Solution: Question 17

The correct option is B.
Temperature scale that registers the freezing point of water as 0 degrees C and the boiling point as 100 degrees C under normal atmospheric pressure. Temperature scale in which zero occurs at absolute zero and each degree equals one kelvin. Water freezes at 273.15 K and boils at 373.15 K.

Important Questions (1 mark): Atoms and Molecules - Question 18
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Avogadro's number represents the number, of atoms in-

Detailed Solution: Question 18

Avogadro's Number and the Number of Atoms:
Avogadro's number, denoted as NA, represents the number of atoms or molecules in one mole of a substance. It is defined as 6.022 x 10^23 particles per mole. Therefore, it can be used to determine the number of atoms in a given amount of a substance.

To determine the correct option, we need to calculate the number of atoms in each given amount of substance and compare it with Avogadro's number.
A: 12g of C12
- The molar mass of carbon is 12 g/mol.
- Since the molar mass and the mass given are the same, we have 1 mole of carbon.
- Therefore, the number of carbon atoms in 12g of C12 is equal to Avogadro's number, 6.022 x 10^23.
B: 320g of sulphur
- The molar mass of sulfur is 32 g/mol.
- To determine the number of moles, we divide the given mass by the molar mass: 320g / 32 g/mol = 10 moles.
- Therefore, the number of sulfur atoms in 320g of sulfur is 10 times Avogadro's number, which is 6.022 x 10^24.
C: 32g of oxygen
- The molar mass of oxygen is 16 g/mol.
- To determine the number of moles, we divide the given mass by the molar mass: 32g / 16 g/mol = 2 moles.
- Therefore, the number of oxygen atoms in 32g of oxygen is 2 times Avogadro's number, which is 1.2044 x 10^24.
D: 12.7g of iodine
- The molar mass of iodine is 127 g/mol.
- To determine the number of moles, we divide the given mass by the molar mass: 12.7g / 127 g/mol = 0.1 moles.
- Therefore, the number of iodine atoms in 12.7g of iodine is 0.1 times Avogadro's number, which is 6.022 x 10^22.
Conclusion:
The correct option is A: 12g of C12. In this case, the number of carbon atoms is equal to Avogadro's number, 6.022 x 10^23.

Important Questions (1 mark): Atoms and Molecules - Question 19
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Molecular mass of ozone is

Detailed Solution: Question 19


To find the molecular mass of ozone, we need to know the atomic masses of the elements present in ozone and their respective proportions.
Ozone (O3) is composed of three oxygen atoms (O). The atomic mass of oxygen is 16 atomic mass units (u).
Therefore, the molecular mass of ozone can be calculated as follows:
Molecular mass of ozone = (Number of oxygen atoms) x (Atomic mass of oxygen)
Molecular mass of ozone = 3 x 16 u
Molecular mass of ozone = 48 u
Therefore, the molecular mass of ozone is 48 u.
Answer: C. 48 u.

Important Questions (1 mark): Atoms and Molecules - Question 20
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Which of the following is not correct according to Dalton's atomic theory?

Detailed Solution: Question 20

The correct option is B.
According to Dalton's atomic theory, all matter, whether an element, a compound or a mixture is composed of small particles called atoms. ... Atoms are indivisible particles, which cannot be created or destroyed in a chemical reaction. Atoms of a given element are identical in mass and chemical properties.

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