Question

The maximum number of molecules is present in :

• A. $15L$ of $H_2$ gas at STP
• B. $5L$ of $N_2$ gas at STP
• C. $0.5g$ of $H_2$ gas
• D. $10g$ of $O_2$ gas

Answer 1

The correct option is A $15L$ of $H_2$ gas at STP

The maximum number of molecules is present in 15 L of $H_2$ gas at STP.

1 mole of a gas at STP occupies a volume of 22.4 L.

15 L of gas corresponds to $\frac{15L}{22.4L}=0.67$ moles.
(B) 5 L of $N_2$ gas at STP :

1 mole of a gas at STP occupies a volume of 22.4 L.

5 L of gas corresponds to $\frac{5L}{22.4L}=0.22$ moles.
(C) 0.5 g of $H_2$ gas (molecular weight 2 g/mol) corresponds to $\frac{0.5g}{2g/mol}=0.25$ moles.
(D) 10 g of $O_2$ gas (molecular weight 3 g/mol) corresponds to $\frac{10g}{32g/mol}=0.3125$ moles.
Higher is the number of moles of a gas, higher will be its number of molecules.

Therefore, the correct option is A.