Answer
$\frac{[H_{2}]^{2}[S_{2}]}{[H_{2}S]^{2}}$
Work Step by Step
The equilibrium constant is the ratio of the concentration of products to the concentration of reactants, each raised to power their stoichiometric coefficients.
Here, the stoichiometric coefficient of $H_{2}$ and $H_{2}S$ is 2. Thus in the expression of the equilibrium constant, they have to be raised to the power 2.
Hence the expression becomes, $\frac{[H_{2}]^{2}[S_{2}]}{[H_{2}S]^{2}}$
