Assertion (A): Sulphur is an octatomic molecule.

Reason (R): The number of atoms in a molecule of an element is known as atomicity.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Both A and R are true but R is not the correct explanation of A.

Explanation — Assertion (A) is true because sulphur molecule (S₈) is composed of eight similar atoms, so it is called Octatomic molecule.

Atomicity is defined as the number of atoms in a molecule of an element.

Therefore, both assertion (A) and reason (R) are true.

However, the reason (R) does not explain why Sulphur is an octatomic molecule.

Hence, both assertion (A) and reason (R) are true but reason (R) does not correctly explain assertion (A).