What are OHactory indicators? Write an activity to prove them.

Explanation

Olfactory Indicators : There are some substances whose odour changes in acidic or basic media. These are called olfactory indicators.
Activity :
Aim : To check the olfactory indicator.
Required materials : 1) Onions 2) Knife 3) Plastic bag 4) Clean clothes.
Procedure :
1)Take some onions and finely chop them.
2) Put the chopped onions in a plastic bag along with some clean cloth.
3) Tie up the bag tightly and keep it overnight in the frtdge. Add acid and base separately to onion pieces.