JEE Main 2024 — Ionic Equilibrium Question with Solution

The correct answer is Option A: Both Statement I and Statement II are correct.

Explanation:

Statement I explains that an aqueous solution of ammonium carbonate is basic. This is because ammonium carbonate ($${\text{(NH}}_4{)}_2{\text{CO}}_3$$) dissociates in water to form ammonium ions ($${\text{NH}}_4^{+}$$) and carbonate ions ($${\text{CO}}_3^{2-}$$). The ammonium ion ($${\text{NH}}_4^{+}$$) is a weak acid and can donate a proton to form ammonia ($${\text{NH}}_3$$) and a hydronium ion ($${\text{H}}_3{\text{O}}^{+}$$), but this happens to a minimal extent due to its weak acidic nature. On the other hand, the carbonate ion ($${\text{CO}}_3^{2-}$$) can accept a hydrogen ion ($${\text{H}}^{+}$$) from water to form bicarbonate ($${\text{HCO}}_3^{-}$$) and hydroxide ions ($${OH}^{-}$$), which makes the solution basic. The reaction of carbonate ions removing hydrogen ions from water is more pronounced than the reaction of ammonium ions donating hydrogen ions to water, hence the overall solution becomes basic.

Statement II is about the general principle that determines the acidic or basic nature of a salt solution formed by the salt of a weak acid and a weak base. The acidic or basic nature of such a salt solution depends on the acid dissociation constant ($$K_a$$) of the acid and the base dissociation constant ($$K_b$$) of the base. If $$K_a>K_b$$, the solution tends to be acidic because the weak acid is stronger (more willing to donate protons) than the weak base is at accepting protons. Conversely, if $$K_b>K_a$$, the solution tends to be basic because the weak base is stronger (more willing to accept protons) than the weak acid is at donating protons. In the case of ammonium carbonate, carbonic acid ($$H_{2}C{O}_3$$) is a weak acid, and ammonia ($$N{H}_3$$) is a weak base. The basic nature of ammonium carbonate solution suggests that the $$K_b$$ of ammonia exceeds the $$K_a$$ of carbonic acid for the reactions in an aqueous solution, making the solution basic.

Therefore, both statements I and II are correct, thereby making Option A the right choice.