#### Answer

$\frac{[C]^{c}[D]^{d}}{[A]^{a}[B]^{b}}$

#### 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,
Products are C and D and their stoichiometric coefficients are c and d respectively.
Reactants are A and B and their stoichiometric coefficients are a and b respectively.
Therefore the expression for equilibrium constant becomes, $\frac{[C]^{c}[D]^{d}}{[A]^{a}[B]^{b}}$.