Concept:A solution with pH less than 7 at equivalence point results when the salt formed undergoes acidic hydrolysis — usually from a strong acid and a weak base.Explanation:Options A, B, and D are reactions between strong acids and strong bases.Their salts do not hydrolyse appreciably, so the pH at equivalence point is 7.For option C: HCl+Mg(OH)2 produces MgCl2.Mg(OH)2 is a weak base, while HCl is a strong acid.The Mg2+ ion hydrolyses in water, releasing H+ ions, making the solution acidic.Therefore, pH < 7.Answer:C. HCl+Mg(OH)2