At 0°C, the density of a certain oxide of a gas at 2 bar is same as that of dinitrogen at 5 bar. What is the molecular mass of the oxide?

$\text{ Density, }\mathrm{d}=\frac{\mathrm{Mp}}{\mathrm{RT}}$

When,T and d are same and R is constant,

$\text{ then }{\mathrm{p}}_1{\mathrm{M}}_1\text{ (gaseous oxide) }={\mathrm{p}}_2{\mathrm{M}}_2\text{ (nitrogen). }$

$2\text{ bar }\times {\mathrm{M}}_1=5\text{ bar }\times 28\mathrm{\mu }\left(\text{ molar mass of }{\mathrm{N}}_2=28\mathrm{\mu }\right)$

Molecular mass of unknown oxide,

${\mathrm{M}}_1=\frac{5\mathrm{bar}\times 28\mathrm{\mu }}{2\mathrm{bar}}=70\mathrm{\mu }$