In a solution, turmeric becomes reddish-brown and red litmus turns blue. Which ion will be in excess?

Correct answer: Hydroxide ion

Reddish-brown turmeric and blue red litmus are both tests for a basic medium. In aqueous school-level chemistry, basicity is associated with an excess of hydroxide ions, OH⁻, over hydrogen ions. Therefore hydroxide ion is the best answer. Hydrogen ions would indicate acidity, whereas chloride and sulphate ions may occur in salts but do not by themselves determine the observed indicator changes. Hence option A is correct.