Equilibrium: JEE Main 2025 Chemistry question

Consider the reaction $\mathrm{X_2Y(g) \rightleftharpoons X_2(g) + \frac{1}{2}Y_2(g)}$. The equation representing correct relationship between the degree of dissociation $(x)$ of $\mathrm{X_2Y(g)}$ with its equilibrium constant Kp is ______. Assume $x$ to be very very small.