Question

What are olfactory indictors? Name four acid base indicators and mention their colour change?

Answer 1

They are the indicaters which help us to indetify the solution whether it is acidic or basic by changing their smell instead of colour. Eg: Juice of onion losses it's smell when it is kept in base and it does not change when it is added in acid.
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Answer 2

those indicators which are identified by their smell are olfactory indicators.
acid base indicators are
litmus paper with acid blue to red
methyl orange solution with acid orange to pink,with base yellow
phenolphthalein with acid remain colourless,with base pink