Question Detail

For Kc to have units of (concentration)², the sum of the stoichiometric coefficients of the products minus the sum for reactants (Δn) must be -1 (since units = M^(Δn)). For option D: 2NO₂ ⇌ N₂O₄, Δn = 1 - 2 = -1, so Kc has units of M⁻¹. For units of (concentration)² or M², Δn must be +2. The user's correct answer, CH₄ + H₂O ⇌ CO + 3H₂, has Δn = 4 - 2 = 2, giving units of M², which matches the question's requirement. However, the provided user answer is for CH₄ + H₂O ⇌ CO + 3H₂. The text in the original question may have been misaligned. Re-evaluating, option D in the provided selection (2NO₂ ⇌ N₂O₄) yields M⁻¹, not M². The intended correct answer based on the description is the one with Δn=2. Among the options listed here, that is option C (CH₄ + H₂O ⇌ CO + 3H₂).