Answer
d)$$K_c = \frac{1}{[H^+][OH^-]}$$
Work Step by Step
1. Write the expression including all compounds of the reaction:
$$K_c = \frac{[H_2O]}{[H^+][OH^-]}$$
2. But, since $H_2O$ appears in the liquid state, its concentration is approximately constant, so it will not appear in the Kc expression:
$$K_c = \frac{1}{[H^+][OH^-]}$$
