Chemistry - Chemical Equilibrium Question with Solution | TestHub

(P) $H_{2}O(l)\rightleftharpoons H_{2}O(g)$: Adding pure liquid water does not change its active mass, so equilibrium does not shift (2), and the product concentration remains constant (4).

(Q) $I_3^{-}(aq)\rightleftharpoons I_2(aq)+I^{-}(aq)$: Adding water dilutes the solution, shifting the equilibrium toward more aqueous particles, which favors the forward reaction (1).

(R) $2AB(g)\rightleftharpoons A_2(g)+B_2(g)$: Increasing volume does not shift equilibrium since $\Delta n_g=0$ (2), but it decreases the concentration of all products due to a larger volume (3).

(S) $A_2(g)\rightleftharpoons 2A(g)$: A catalyst does not alter the equilibrium position (2), keeping product concentrations constant (4).

Since (Q) shifts forward and does not match (4), option (A) contains the only incorrect set of matches.

Correct Answer: (A)