NCERT Chemistry: Some Basic Concepts of Chemistry MCQ Quiz

Question 1

A sample contains 3.011 × 10^23 molecules of oxygen gas. How many moles of O2 are present?

Accepted Answer

0.25 mol

Answer

0.50 mol

Answer

1.00 mol

Answer

2.00 mol

Question 2

Which statement best explains why the law of definite proportions holds for water prepared from different sources?

Accepted Answer

Water samples always contain identical dissolved impurities

Answer

Hydrogen and oxygen always combine in a fixed mass ratio in water

Answer

The volume ratio of hydrogen and oxygen changes with location

Answer

The isotopic composition removes all mass variation

Question 3

The mass percentage of oxygen in H2SO4 is closest to:

Answer

32.7%

Answer

49.0%

Answer

65.3%

Answer

98.0%

Question 4

When 12 g of carbon combines completely with 32 g of oxygen, the compound formed is:

Answer

CO

Answer

CO2

Answer

C2O3

Answer

C3O2

Question 5

A compound contains 40% carbon, 6.7% hydrogen and 53.3% oxygen by mass. Its empirical formula is:

Answer

CH2O

Answer

C2H4O2

Answer

CHO

Answer

CH3O

Question 6

If the empirical formula of a compound is CH2O and its molar mass is 180 g mol−1, the molecular formula is:

Answer

C4H8O4

Answer

C5H10O5

Answer

C6H12O6

Answer

C3H6O3

Question 7

Which pair of quantities is numerically equal for 18 g of water?

Answer

Number of molecules and molar mass

Answer

Number of moles and Avogadro constant

Answer

Molar mass and gram molecular mass value

Answer

Atomicity and number of moles

Question 8

The number of atoms present in 0.25 mol of methane (CH4) is:

Answer

1.5055 × 10^23

Answer

3.011 × 10^23

Answer

7.5275 × 10^23

Answer

1.2044 × 10^24

Question 9

Which law is most directly illustrated when nitrogen monoxide and nitrogen dioxide show different masses of oxygen combining with the same mass of nitrogen?

Answer

Law of conservation of mass

Answer

Law of multiple proportions

Answer

Law of reciprocal proportions

Answer

Gay-Lussac's law of combining volumes

Question 10

A hydrated salt loses 36 g of water on heating and leaves 80 g of anhydrous salt. The percentage of water in the original sample is:

Answer

25.0%

Answer

31.0%

Answer

36.0%

Answer

45.0%

Question 11

One main reason Dalton's atomic theory required modification was that it could not account for:

Answer

The existence of isotopes of the same element

Answer

The conservation of mass in chemical reactions

Answer

The formation of simple compounds

Answer

The combining of atoms in whole numbers

Question 12

How many moles of sodium atoms are present in 11.7 g of sodium?

Answer

0.25 mol

Answer

0.50 mol

Answer

0.75 mol

Answer

0.51 mol

Question 13

A mixture contains 4 g H2 and 32 g O2. After complete reaction, which statement is correct?

Answer

Both reactants are fully consumed

Answer

Hydrogen remains in excess

Answer

Oxygen remains in excess

Answer

Water cannot form due to unequal masses

Question 14

The mass of one atom of sodium is closest to:

Answer

3.82 × 10^−23 g

Answer

6.02 × 10^23 g

Answer

23.0 × 10^−23 g

Answer

1.91 × 10^−22 g

Question 15

Which sample contains the greatest number of molecules?

Answer

2 g of H2

Answer

16 g of O2

Answer

18 g of H2O

Answer

28 g of N2

Question 16

A compound has vapour density 44 relative to hydrogen. Its molar mass is:

Answer

22 g mol−1

Answer

44 g mol−1

Answer

88 g mol−1

Answer

176 g mol−1

Question 17

If 0.2 mol of calcium carbonate decomposes completely, the amount of carbon dioxide formed is:

Answer

4.4 g

Answer

8.8 g

Answer

10.0 g

Answer

20.0 g

Question 18

Which expression correctly gives the number of formula units in 0.1 mol of NaCl?

Answer

0.1 / 6.022 × 10^23

Answer

6.022 × 10^22

Answer

1.2044 × 10^24

Answer

3.011 × 10^23 / 10^2

Question 19

In a reaction, 5.6 g of iron combines with sulfur to form 8.8 g of iron sulfide. The mass of sulfur that reacted is:

Answer

1.6 g

Answer

2.4 g

Answer

3.2 g

Answer

14.4 g

Question 20

Which observation most strongly supports the law of conservation of mass in a precipitation reaction?

Answer

The precipitate color remains constant in sunlight

Answer

The total mass stays unchanged in a closed flask

Answer

The solution volume decreases after mixing

Answer

The reaction finishes faster on stirring

NCERT Chemistry: Some Basic Concepts of Chemistry MCQ Quiz

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