SSC Selection Post 2020 PYQ — Question 36

The correct answer is option 4 i.e. Onion.

Onion can be used as an 'olfactory indicator'. An olfactory indicator is a substance whose smell or odor changes when it comes into contact with an acidic or basic solution.When a basic solution (like sodium hydroxide) is added to a cloth strip treated with onion extract, the characteristic pungent smell of the onion tends to diminish or completely disappear. However, when an acidic solution (like hydrochloric acid) is added, the onion's smell generally remains unchanged. This distinct change or lack thereof in its odor allows onion to indicate the presence of an acid or a base.