Vanilla essence, onion and clove oil can be used to test whether a substance is an acid or a base, because their odour changes in acidic or basic media. What are such substances called?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Olfactory indicators
Substances whose odour changes in an acidic or a basic medium are called olfactory indicators. For example, the smell of onion and vanilla cannot be detected in a basic solution.