For the reaction, $SO_{2(g)} + \frac{1}{2}O_{2(g)} \leftrightharpoons SO_{3(g)}$, if $K_P = K_C(RT)^x$ where the symbols have usual meaning then the value of $x$ is: (assuming ideality)

Question

( A ) $-\frac{1}{2}$
( B ) $-1$
( C ) $1$
( D ) $\frac{1}{2}$