Question

which of the following contains same number of molecules as 9 gram of water?

a) 2 gram of hydrogen gas

b) 14 gram of nitrogen gas

c) 32 gram of oxygen gas

d) 44 grams of CO2

(with a brief reason for ur answer)

Answer 1

Answer- The above question is from the chapter 'Some Basic Concepts of Chemistry'.

Concept Used: 1) Number of moles = $\frac{Given \: mass}{Molar \: mass}$

2) No. of molecules = Number of moles × Avogadro's Number

(Let Avogadro's Number be N.)

Given question: Which of the following contains same number of molecules as 9 gram of water?

a) 2 gram of hydrogen gas

b) 14 gram of nitrogen gas

c) 32 gram of oxygen gas

d) 44 grams of CO₂

(with a brief reason for your answer.)

Answer: For 9 gram of water,

No. of moles = $\frac{9}{18}$ = $\frac{1}{2}$

No. of molecules = $\frac{N}{2}$

a) For 2 gram of hydrogen gas,

No. of moles = $\frac{2}{2}$ = 1

No. of molecules = N

which is not equal to number of molecules in 9 gram of water.

b) For 14 gram of nitrogen gas,

No. of moles = $\frac{14}{28}$ = $\frac{1}{2}$

No. of molecules = $\frac{N}{2}$

which is equal to number of molecules in 9 gram of water.

c) For 32 gram of oxygen gas,

No. of moles = $\frac{32}{32}$ = 1

No. of molecules = N

which is not equal to number of molecules in 9 gram of water.

d) For 44 grams of CO₂,

No. of moles = $\frac{44}{44}$ = 1

No. of molecules = N

which is not equal to number of molecules in 9 gram of water.

∴ b) 14 gram of nitrogen gas is the correct answer.