A mixture of hydrogen and oxygen has volume 500 cm³, temperature 300K, pressure 400kPa and mass 0.76g. The ratio of masses of oxygen to hydrogen will be:

From, ideal gas equation PV=nRT 

${\text{400\hspace{0.17em}×\hspace{0.17em}10}}^{\text{3}}{\text{\hspace{0.17em}×\hspace{0.17em}500\hspace{0.17em}×\hspace{0.17em}10}}^{\text{-6}}\text{\hspace{0.17em}=\hspace{0.17em}n}\left(\frac{\text{25}}{\text{3}}\right)\left(\text{300}\right)$

$\Rightarrow \text{\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}n\hspace{0.17em}=\hspace{0.17em}}\frac{\text{2}}{\text{25}}$

Let n₁ and n₂ be no. of moles of hydrogen & oxygen respectively. 

Also, n₁ + n₂ = n 

using  $\text{n\hspace{0.17em}=}\frac{\text{m}}{\text{M}}$

$\frac{{\text{m}}_{\text{1}}}{\text{2}}\text{+}\frac{{\text{m}}_{\text{2}}}{\text{32}}\text{=}\frac{\text{2}}{\text{25}}$ and m₁ + m₂ =0.76gm 

$\frac{{\text{m}}_{\text{2}}}{{\text{m}}_{\text{1}}}\text{=}\frac{\text{16}}{\text{3}}$