A salt solution turns blue litmus red. From which type of acid and base is it most likely formed?

Correct answer: Strong acid and weak base

Blue litmus turning red means the salt solution is acidic. In the usual school-level classification, salts of strong acids and weak bases undergo hydrolysis that increases the hydrogen-ion concentration, producing an acidic solution. Hence option B is the most likely combination. A strong acid–strong base salt is generally neutral, while a weak acid–strong base salt is generally basic; weak–weak salts require comparison of strengths.