The reaction, ${\mathrm{PCl}}_5 \rightleftharpoons {\mathrm{PCl}}_3 + {\mathrm{Cl}}_2$  is started in a 5 litre container by taking one mole of ${\mathrm{PCl}}_5.$ If 0.3 mole of ${\mathrm{PCl}}_5$ is there at equilibrium, concentration of ${\mathrm{PCl}}_3$ and ${\mathrm{K}}_{\mathrm{C}}$ will respectively be

${\mathrm{PCl}}_5$      $\rightleftharpoons$           ${\mathrm{PCl}}_3$      +        ${\mathrm{Cl}}_2$

1                              0                      0       Initial mole

$\frac{1 - 0.7}{5}$               $\frac{0.7}{5}$                 $\frac{0.7}{5}$  Conc. at equilibrium

Total mole of ${\mathrm{PCl}}_3$ = 0.7

Concentration = 0.14

${\mathrm{K}}_{\mathrm{C}}$ = $\frac{{\mathrm{x}}^2}{\left(1-\mathrm{x}\right)\mathrm{V}}= \frac{0.7 \times 0.7}{0.3 \times 5}= \frac{49}{150}=0.326$