Which of the following physical quantities has neither dimensions nor unit ?

Options

A. Angle
B. Luminous intensity
C. Coefficient of friction
D. Current

Answer

C

Explanation

Unit less physical quantities are always dimensions. For example, refractive index and relative density. These quantities are the ratio of same physical quantities.
A dimensionless physical quantity may have a unit. For example, plane angle and solid angle.The unit of plane angle is radian but it is dimensionless.
Now
Coefficient of friction`=("friction force")/("Normal reaction")`
`=([MLT^(-2)])/([MLT^(-2)])=` no dimensions
Unit`=N/N=`no unit
The coefficient of friction is theratio fo two forces. Hence it is dimensionless. it also don.t have any unit.