Which of the following is proportional to the net external force acting on a body?

a. speed

b. velocity

c. rate of change of speed

d. rate of change of velocity

The option which is directly proportional to the net external force acting on a body is: D. Rate of change of velocity.

Newton's Second Law of Motion states that the net external force acting on a physical object is directly proportional to the acceleration of the physical object and inversely proportional to its mass.

Mathematically, Newton's Second Law of Motion is given by the formula;

However, acceleration can be defined as the rate of change of velocity with respect to time. Thus, acceleration is the same as the rate of change of velocity.

In conclusion, the rate of change of velocity (acceleration) is directly proportional to the net external force acting on a body in accordance with Newton's Second Law of Motion.

Read more here: link