If a solution does not change either red or blue litmus, which test can give more clarity?

Correct answer: Checking pH with universal indicator

Red and blue litmus provide only a broad classification and may show little or no change for a nearly neutral solution or a weak substance. A universal indicator gives a range of colours corresponding to approximate pH values, so it provides more information. Option A is correct. Tasting, rubbing, or putting an unknown solution in the eye is unsafe and scientifically invalid.