The S.I unit of velocity is:
A. km/h
B. m/min
C. km/min
D. m/s

Hint: First figure out the definition of the velocity from that make the equation for velocity, after writing the equation figure out the units with the aspect of equation for velocity then place the unit as the variables according to the equation.

Complete step by step answer:
The velocity of an object is the rate of change of position with respect to frame of reference which is a function of time.
Therefore according to the question:
V=s/t,
s is the displacement, t is the time.
SI unit of s is m,
SI unit of t is sec,
Therefore the unit of velocity (V) is m/s.
Hence option D is the correct option.

Additional Information:
Some units that identify velocity are,
Kilometers per hour, Knot (unit), Feet per minute, Foot per second, Meter per hour, Miles per hour, Inch per second, Speed of light.
The magnitude of velocity can also be expressed in centimeters per second (cm/s).
The rate of change of velocity with respect to time is known as acceleration.
The ratio of change in velocity during a given time interval such that the time interval goes to zero is known as instantaneous acceleration.
The rate of change of angular position of a rotating body is known as angular velocity.

Note: Speed and velocity should not be confused. There is a great difference between them, for example, velocity tells us about the speed of the object and also in which direction the object is moving while speed only gives us an idea of how fast the object is moving and not in which direction.