An open vessel containing air is heated from 300 K to 400 K. The fraction of air originally present which goes out of it is

On heating the gas in open vessel

$$\begin{gathered} \frac{\text{PV}}{\text{R}}={\text{nT ; n}}_1{\text{T}}_1{\text{=n}}_2{\text{T}}_2 \\ \therefore \frac{{\mathrm{n}}_1}{{\mathrm{n}}_2}=\frac{4}{3}\text{ or }{\mathrm{n}}_2=\frac{3}{4}{\mathrm{n}}_1 \\ \mathrm{Gas} \mathrm{expelled}=1-\frac{3}{4}{\mathrm{n}}_1=\frac{1}{4}{\mathrm{n}}_1 \end{gathered}$$
Thus, $\frac{{\mathrm{n}}_1}{4}$ gas is given out.