Which of the following physical quantity is fundamental? (a) viscosity (b) velocity (c) force (d) time

Fundamental quantities are basic quantities that cannot be defined in terms of other physical quantities. Derived quantities can be expressed as a combination or product of fundamental quantities.

Now, let's analyze each of the given options to see which one is a fundamental quantity: (a) Viscosity: It is a measure of a fluid's resistance to flow and depends on factors like temperature and pressure. It is a derived quantity since it can be expressed as a combination of mass (M), length (L), and time (T). (b) Velocity: It is a vector quantity representing the rate of change of an object's position with respect to time. It is a derived quantity, as it can be expressed as length (L) divided by time (T). (c) Force: It is a vector quantity that represents the interaction between two objects and causes acceleration. According to Newton's second law, force is equal to mass (M) times acceleration (L/T^2). Hence, it is a derived quantity. (d) Time: It is a scalar quantity that represents the duration or interval between two events. It cannot be expressed as a combination or product of other physical quantities. Therefore, time is a fundamental quantity.

Based on the analysis of each option, we can conclude that among the given physical quantities, time (option d) is the fundamental quantity.