Question

the substance that change their odour in the presence of an acid or base is known as

Answer 1

All onion,clove oil and vanilla extract are examples. An olfactory indicator works on the principle that when an acid or base is added to it,then different odour can be detected in bases whereas odour remains same in acids.Certain substances changes odour in acidic or basic medium

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Answer 2

Hey mate..
Ur answer is olfactory indicators.
hope it helps u.