The correct answer is (c) NaHSO4. An acid salt is a salt that is derived from the partial neutralization of an acid, resulting in a substance that has both acidic and basic properties. NaHSO4 is an example of an acid salt because it is derived from the partial neutralization of sulfuric acid (H2SO4) with sodium hydroxide (NaOH). It has acidic properties because it can donate a hydrogen ion (H+) in water, and it has basic properties because it can accept a hydrogen ion (H+) in the presence of a strong acid. The other options are not acid salts. CH3COOONa is a salt of a weak acid (acetic acid) and a strong base (sodium hydroxide), and therefore it is a basic salt. Mg(OH)Cl is a salt of a strong base (magnesium hydroxide) and a strong acid (hydrochloric acid), and therefore it is a neutral salt. (NH4)2SO4 is a salt of a weak base (ammonia) and a strong acid (sulfuric acid), and therefore it is an acidic salt.