An open flask containing air is heated from 300 K to 500 K. What percentage of air will be escaped to the atmosphere, if pressure is keeping constant?

${\mathrm{V}}_1=\mathrm{V},{\mathrm{T}}_1=300\mathrm{K},{\mathrm{T}}_2=500\mathrm{K},{\mathrm{V}}_2=?$
At constant pressure ${\mathrm{V}}_1{\mathrm{T}}_2={\mathrm{V}}_2{\mathrm{T}}_1$
$\therefore {\mathrm{V}}_2=\frac{{\mathrm{V}}_1{\mathrm{T}}_2}{{\mathrm{T}}_1}=\frac{\mathrm{V}\times 500}{300}=\frac{5\mathrm{V}}{3}$
$\therefore$Volume of air escaped = final volume - initial volume
      $=\frac{5\mathrm{V}}{3}-\mathrm{V}=\frac{2\mathrm{V}}{3}$
$\therefore \mathrm{\%}\text{ of air escaped }=\frac{2\mathrm{V}/3}{5\mathrm{V}/3}\times 100=40\mathrm{\%}$