The equilibrium constant for the equilibrium $2HX_{(g)} \rightleftharpoons H_{2(g)} + X_{2(g)}$ is $1 \times 10^{-5}$. What will be the equilibrium concentration of $HX$ if the equilibrium concentrations for $H_2$ and $X_2$ are $1.2 \times 10^{-3} \ M$ and $1.2 \times 10^{-4} \ M$ respectively?

• A
  $12 \times 10^{-4} \ M$
• B
  $12 \times 10^{-3} \ M$
• C
  $12 \times 10^{-2} \ M$
• D
  $12 \times 10^{-1} \ M$