Initially a gas of diatomic molecules is contained in a cylinder of volume V 1 at a pressure P 1 and…

$P_1=P_1$
$v_1=v_1$
$T_1=250$
$n_1=n_0$
${\mathrm{n}}_2=0.75{\mathrm{n}}_0+2\times 0.25{\mathrm{n}}_0=1.25\mathrm{no}$
$v_2=2V_1$
$T_2=2000$
${\mathrm{P}}_1{\mathrm{V}}_1={\mathrm{n}}_1{\mathrm{RT}}_1$
${\mathrm{P}}_2{\mathrm{V}}_2={\mathrm{n}}_2{\mathrm{RT}}_2$
${\mathrm{P}}_1{\mathrm{V}}_1={\mathrm{n}}_0\mathrm{R}\times 250$
$P_2\left(2V_1\right)=\left(.25{\mathrm{n}}_0\mathrm{R}\left(2000\right)\right)$
equation $\left(1\right) /\left(2\right)$
$\frac{P_1}{2P_2}=\frac{250}{1.25\times 2000}$
$\frac{P_1}{P_2}=\frac{1}{5}$
$\frac{P_2}{P_1}=5$