$32g$ of oxygen and $3g$ of hydrogen are mixed and kept in a vessel at $760mm$ pressure and $0^{\circ }C$. The total volume occupied by the mixture will be nearly:

The correct option is D $56litre$

Ideal gas law is given by,

$PV=nRT$

where $P=760mm,Hg=1atm,V=?$

$n=$ moles of $O_2+$ moles of $H_2$

$=\left(\frac{32}{32}\right)+\left(\frac{3}{2}\right)=2.5$ moles

$R=0.08205L\cdot atm/molk,T=273K$

$V=\frac{nRT}{P}=\frac{2.5\times 0.082\times 273}{1}$

$\Rightarrow V=56L$

Hence, the correct answer is option $\text{D}$.