Autoionization of water is endothermic

Steps:

• The autoionization equilibrium H₂O ⇌ H⁺ + OH⁻ is endothermic, so increasing temperature shifts it right per Le Chatelier's principle.
• This increases [H⁺] and [OH⁻] equally, raising Kw but keeping [H⁺] = [OH⁻] = 10⁻⁷ M at neutrality.
• pH remains 7, so water stays neutral.
• Thus, only more ionization occurs, without acidity or alkalinity.

Why D is correct:

• Increasing temperature favors the endothermic forward reaction, ionizing more molecules while maintaining equal [H⁺] and [OH⁻] for neutrality (Kw increases symmetrically).

Why the others are wrong:

• A is wrong because water does not become acidic ([H⁺] rises but equals [OH⁻]).
• B is wrong because water remains neutral, not acidic.
• C is wrong because water does not become alkaline ([OH⁻] rises but equals [H⁺]).

Final answer: D