Final answer:
The equilibrium constant expression for the reaction 2Cu → Cu₂ is [Cu₂]/[Cu]², given that solids are not included in Kc expressions and assuming that Cu₂ is not a solid.
Step-by-step explanation:
The equilibrium constant expression for the reaction 2Cu → Cu₂ can be constructed based on the stoichiometry of the reaction.
Given that the reaction involves solid copper turning into a copper dimer, we consider only the species whose concentrations change with the progression of the reaction.
Since pure solids and liquids do not appear in the equilibrium constant expression, and assuming the copper dimer is not a solid, the correct expression for the equilibrium constant Kc would be [Cu₂]/[Cu]2.