Question

Those substances whose smell (or odour) changes in acidic or basic solutions are called ______ indicators.

Answer 1

Those substances whose smell (or odour) changes in acidic or basic solutions are called olfactory indicators.

Explanation:

Olfactory indicators rely on the sense of smell rather than sight to signal a change in pH. When these substances react with an acid or a base, a chemical reaction alters the shape of their odour-producing molecules. This structural change neutralises or modifies their natural scent, making them highly useful testing tools for visually impaired individuals.