Given:
Objective: Determine the equilibrium constant \( K_c \) in the presence of a catalyst at the same temperature.
The equilibrium constant \( K_c \) for the reaction: \[ A_2(g) + B_2(g) \rightleftharpoons 2AB(g) \] is given by: \[ K_c = \frac{[AB]^2}{[A_2][B_2]} \]
The presence of a catalyst affects the rate of reaction but does not change the equilibrium constant. Therefore, the equilibrium constant \( K_c \) remains: \[ \boxed{2 \times 10^{-5}} \]