In a solution both red and blue litmus do not change colour. What is the most appropriate conclusion?

Correct answer: The solution may be neutral

The governing concept is the behaviour of acid–base indicators. An acid changes blue litmus to red, while a base changes red litmus to blue. If neither paper changes colour, the solution is consistent with a neutral solution, although this observation alone may not establish exact pH. It cannot prove a strong acid or base, and a solution is not necessarily a gas. Thus A is the most appropriate conclusion.