Phosphorus pentachloride dissociates as follows,in a closed reaction vessel:
$PCl_{5(g)} \rightleftharpoons PCl_{3(g)} + Cl_{2(g)}$
If total pressure at equilibrium of the reaction mixture is $P$ and degree of dissociation of $PCl_5$ is $x,$ the partial pressure of $PCl_3$ will be:

• A
  $\left( \frac{x}{x - 1} \right) P$
• B
  $\left( \frac{x}{1 - x} \right) P$
• C
  $\left( \frac{x}{1 + x} \right) P$
• D
  $\left( \frac{2x}{1 - x} \right) P$