Which among the following salts turns red litmus blue in its aqueous solution?

Step-by-step solution

The salt that turns red litmus blue must produce a basic aqueous solution, which occurs when hydrolysis yields hydroxide ions. This requires a salt derived from a strong base and a weak acid. For potassium cyanide (KCN), formed from strong base KOH and weak acid HCN, the cyanide ion hydrolyzes: CN ^- + H ₂ O HCN + OH ^- , producing basic solution. In contrast, NaN O₃ , NaCl, and KCl derive from strong acids and strong bases, undergo no significant hydrolysis, and yield neutral solutions. Thus, only KCN turns red li