Question

The aqueous solution of one of the following salts will turn red litmus to blue. This salt is:
(a) potassium sulphate
(b) sodium sulphate
(c) sodium chloride
(d) potassium carbonate

Answer 1

potassium carbonate      
Potassium carbonate (K₂CO₃) is formed from a weak acid, carbonic acid (H₂CO₃), and a strong base, potassium hydroxide (KOH). On hydrolysis, K₂CO₃ forms more OH^- ions than H⁺ ions. Thus, it is basic and therefore turns red litmus blue.