Final answer:
The equilibrium expression for the reaction Hg(l) + Hg2+(aq) = Hg22+ (aq) is K = [Hg22+], excluding liquid mercury from the expression.
Step-by-step explanation:
The correct equilibrium expression for the reaction where metallic mercury reacts with a solution of mercury(I) nitrate to form mercury(I) ion, Hg22+(aq), is based on excluding pure solids and liquids, as these do not have variable concentrations.
Considering the given reaction, Hg(l) + Hg2+(aq) = Hg22+ (aq), the equilibrium expression would not include mercury in its liquid state. Therefore, the equilibrium constant (K) expression for the above equation is given by:
K = [Hg22+]
Where [Hg22+] represents the aqueous concentration of the mercury(I) ion. There is no denominator in this expression because the reactant, metallic mercury, is in a pure liquid state, and thus its concentration is constant and not part of the equilibrium expression.