The equilibrium pressure of ${\mathrm{NH}}_4{\mathrm{CN}}_{\left(\mathrm{S}\right)}\rightleftharpoons {\mathrm{NH}}_{3\left(\mathrm{g}\right)}+{\mathrm{HCN}}_{\left(\mathrm{g}\right)}$ is 4 atm. In an experiment, if ${\mathrm{NH}}_4{\mathrm{CN}}_{\left(\mathrm{s}\right)}$ is allowed to decompose in presence of ${\mathrm{NH}}_3$ at 3 atm, then

pressure of HCN = 1atm (at new equilibrium state)

pressure of ${\mathrm{NH}}_3=4 \mathrm{atm}$ (at new equilibrium state)

pressure of HCN = 2atm (at old equilibrium state)

Kp = 4