To determine which of the given options is NOT a fundamental S.I. unit, we need to first understand what the fundamental S.I. units are. The International System of Units (S.I.) defines seven fundamental units, which are the basic units for measurement in science and engineering. These units and their corresponding physical quantities are:
1. Length: Metre (m)
2. Mass: Kilogram (kg)
3. Time: Second (s)
4. Electric current: Ampere (A)
5. Temperature: Kelvin (K)
6. Amount of substance: Mole (mol)
7. Luminous intensity: Candela (cd)
Given these fundamental units, let's analyze the options provided in the question:
(a) Metre - As per the list of fundamental units, the metre (m) is the fundamental unit for length.
(b) Ampere - The ampere (A) is the fundamental unit for electric current.
(c) Kelvin - The kelvin (K) is the fundamental unit for temperature.
(d) Radian - The radian is a unit of plane angle, but it is not one of the seven fundamental S.I. units. Instead, it is a derived unit.
Upon examining the options, it is clear that:
- Metre, Ampere, and Kelvin are all fundamental S.I. units.
- Radian, on the other hand, is not a fundamental S.I. unit.
Thus, the option that is NOT a fundamental S.I. unit is:
(d) Radian
