Phosgene gas $\left(COC{l}_2\right)$  dissociates to carbon  monoxide gas and chlorine gas with a change of pressure from 450 mm Hg to 600 mm Hg. If volume and temperature remain constant throughout the experiment. The value of $K_p$ (mm of Hg) is 

                                        $COC{l}_2\left(g\right)\underset{ }{\rightleftharpoons }CO\left(g\right)+C{l}_2\left(g\right)$               
At  $t=0,450mmHg --$
At Eqm,               450-p                                           p          p
 $\Rightarrow 450-p=600$
 $\Rightarrow p=150$
 $K_p=\frac{150\times 150}{300}=75$