General Science

Correct answer: Odour

Explanation:
An olfactory indicator is a substance whose odour changes in acidic or basic solutions. This change in smell is used to detect whether a substance is acidic or basic.

Common olfactory indicators include:
- Onion extract
- Clove oil
- Vanilla essence

These substances have a characteristic smell that either fades or changes in acidic or basic environments.

Hence, the correct answer is: Odour.

Tooth enamel is primarily composed of calcium phosphate, specifically in the form of hydroxyapatite. This mineral makes up about 95% of the enamel, giving it strength and hardness.

The correct option is (B): calcium phosphate

Tooth enamel is primarily made up of calcium phosphate, a mineral compound. It is the hardest substance in the human body and plays a crucial role in protecting teeth from decay and damage.
Thus, the correct answer is calcium phosphate.