A mixture of gases at 760 mm pressure contains 65%  nitrogen, 15%  oxygen and 20%   carbon dioxide by volume. What is partial pressure of ${\mathrm{O}}_2$ in nm?

The formula used to find partial pressure is

Patrial pressure of gas = mole fraction of a gas ×total pressure of mixture

Total no. of moles = 15+65+20 =100

Total pressure = 760 mm of Hg

${\mathrm{P}}_{{\mathrm{O}}_2}=\frac{15}{100}\times 760=114 \mathrm{mm} \mathrm{og} \mathrm{Hg}$

  Partial pressure of ${\mathrm{O}}_2=114 \mathrm{mm} \mathrm{og} \mathrm{Hg}$