Final answer:
The correct expression for the equilibrium constant Kc of the reaction 2 c (aq) + d (aq) ⇌ 2 a (aq) + b (aq) is Kc = [a]^2[b] / [c]^2[d].
Step-by-step explanation:
The correct expression for the concentration based equilibrium constant for the given chemical reaction 2 c (aq) + d (aq) ⇌ 2 a (aq) + b (aq) can be derived from the general equilibrium expression. According to the rules for writing equilibrium constant expressions, products are placed in the numerator and reactants in the denominator of the expression, with each concentration raised to the power of its respective coefficient in the balanced chemical equation. Therefore, the correct expression for the equilibrium constant, Kc, for this reaction is Kc = [a]2[b] / [c]2[d].