Consider the following reactions in which all the reactants and products are present in gaseous state:
$2xy \rightleftharpoons x_2 + y_2$ $K_1 = 2.5 \times 10^5$
$xy + \frac{1}{2}z_2 \rightleftharpoons xyz$ $K_2 = 5 \times 10^{-3}$
The value of $K_3$ for the equilibrium $\frac{1}{2}x_2 + \frac{1}{2}y_2 + \frac{1}{2}z_2 \rightleftharpoons xyz$ is:

• A
  $2.5 \times 10^{-3}$
• B
  $2.5 \times 10^3$
• C
  $1.0 \times 10^{-5}$
• D
  $5 \times 10^{-3}$