Consider the following equilibrium: $2H_2(g) + X_2(g) \rightleftharpoons 2H_2X(g) + energy$
Addition of $X_2$ to a system described by the above equilibrium
will cause $[H_2]$ to decrease
will cause $[X_2]$ to decrease
will cause $[H_2X]$ to decrease
will have no effect
cannot possibly be carried out