Which of the following is unitless quantity?A. Pressure gradientB. Displacement gradientC. Force gradientD. Velocity gradient

A unitless quantity is a quantity that does not have any units associated with it. Let's examine each of the options:

A. Pressure gradient: The units of pressure gradient are typically pascals per meter (Pa/m) or some other unit of pressure per unit length. Therefore, pressure gradient is not unitless.

B. Displacement gradient: The displacement gradient measures the change in displacement per unit length. Its units are typically meters per meter (m/m) or some other unit of length per unit length. Therefore, displacement gradient is not unitless.

C. Force gradient: The force gradient is a measure of how force changes with respect to a change in position. Its units would be newtons per meter (N/m) or some other unit of force per unit length. Therefore, force gradient is not unitless.

D. Velocity gradient: The velocity gradient measures how velocity changes with respect to a change in position. Its units are typically meters per second per meter (m/s/m) or some other unit of velocity per unit length. Therefore, velocity gradient is not unitless.

None of the options provided (A, B, C, D) represents a unitless quantity.