Initially a gas of diatomic molecules is contained in a cylinder of volume $V_1$ at a pressure $P_1$ and temperature $250 \mathrm{K}$. Assuming that $25\%$ of the molecules get dissociated causing a change in number of moles. The pressure of the resulting gas at temperature $2000 \mathrm{K},$ when contained in a volume $2{\mathrm{V}}_1$ is given by ${\mathrm{P}}_2$. The ratio ${\mathrm{P}}_2/{\mathrm{P}}_1$ is -