Question

5.6 litres of a gas weighs $1\text{g}$ at STP. The gas can be:

• A. $H_2$
• B. $N_2$
• C. $He$
• D. $O_2$

Answer 1

The correct option is C $He$

Number of moles of gas $\frac{5.6}{22.4}=\frac{1}{4}$

$\text{Number of moles}=\frac{\text{Weight}}{\text{Molecular weight}}$

$=\frac{1}{4}=\frac{1}{\text{Molecular weight}}\Rightarrow \text{Molecular weight}=4$

Molecular weight 4 is possible only for He out of the given options. Hence, the answer is (c)