Answer
a) equilibrium constant $ k = \frac{[N_{2}O_{4}]}{[NO_{2}]^{2} }$
b) equilibrium constant $ k = \frac{[NO]^{2}[Br_{2}]}{[BrNO]^{2} }$
c) equilibrium constant $ k = \frac{[H_{2}][CO_{2}] }{[H_{2}O][CO]}$
d) equilibrium constant $ k = \frac{[CS_{2}][H_{2}]^{4}}{[CH_{4}][H_{2}S]^{2}}$
Work Step by Step
For any reaction say, $aX \leftrightharpoons bY$ where X is reactant and Y is product and a & b are the stoichiometric co-efficients we can write equilibrium expression as follows:
$k = \frac{[Y]^{b}}{[X]^{a}}$
Here [Y] means equilibrium concentration of the product Y.
and [X] means equilibrium concentration of the reactant X.
