At a given temperature,the equilibrium constant for the reaction $PCl_{5(g)} \rightleftharpoons PCl_{3(g)} + Cl_{2(g)}$ is $2.4 \times 10^{-3}$. At the same temperature,the equilibrium constant for the reaction $PCl_{3(g)} + Cl_{2(g)} \rightleftharpoons PCl_{5(g)}$ is:

• A
  $2.4 \times 10^{-3}$
• B
  $-2.4 \times 10^{-3}$
• C
  $4.17 \times 10^{2}$
• D
  $4.8 \times 10^{-2}$