Question

Weak organic compounds which change their colour in accordance with pH are known as:
(A) Desiccators
(B) Indicators
(C) Olfactory substances
(D) None of the above

Answer 1

pH is defined as the negative logarithm of the hydrogen ion concentration $\left( {{H^ + }} \right)$ . acids have lower values of pH, whereas basic compounds have higher values of pH, and neutral compounds like water have a pH equal to $7$ . Some chemical compounds change their colour according to pH value.

Complete answer:
Desiccators are the closed systems that consist of chemical substances like calcium chloride and other drying agents to absorb the moisture from the chemical compounds.
Indicators are the chemical compounds that are known as weak organic acids or bases that change their colour according to pH. Thus, these are known as acid-base indicators simply known as indicators. Some of the examples of synthetic indicators were phenolphthalein indicator, methyl orange and litmus paper. Some of the examples of natural indicators were turmeric, grape juice, and red cabbage. The main use of indicators was to detect the range of pH present in the chemical compounds.
The chemical substances whose smell changes in presence of acidic or basic compounds are known as olfactory substances.
Thus, weak organic compounds which change their colour in accordance with pH are known as indicators.
Option B is the correct one.

Note:
When olfactory substances are kept in contact with onion or vanilla extracts. Then the smell of these substances i.e., onion smell and vanilla extract can be changed or disappeared. When sodium hydroxide is added to a cloth that has an onion smell, then the onion smell can disappear.