Definition of Force:
Force is a physical quantity that can change the state of motion or shape of an object. It is a vector quantity, which means it has both magnitude and direction. Force is measured in Newtons (N).

Explanation of the Correct Answer:
The correct answer for the definition of force is option 'B', which states that force is the rate of change of momentum.

Understanding Momentum:
Before discussing the rate of change of momentum, it is important to understand momentum. Momentum is the quantity of motion possessed by an object. It is the product of an object's mass and velocity. Mathematically, momentum (p) can be expressed as:
p = m * v,
where 'm' is the mass of the object and 'v' is its velocity.

Rate of Change of Momentum:
The rate of change of momentum refers to how quickly the momentum of an object changes. It can be calculated by dividing the change in momentum by the time taken. Mathematically, the rate of change of momentum (force) is given by:
F = △p / △t,
where 'F' is the force, △p is the change in momentum, and △t is the change in time.

Relation between Force and Momentum:
From the equation F = △p / △t, it can be observed that force is directly proportional to the rate of change of momentum. This means that a greater force is required to change the momentum of an object quickly, while a smaller force is sufficient for a slower change in momentum.

Implication of the Definition:
The definition of force as the rate of change of momentum implies that when a force is applied to an object, it will cause a change in momentum. This change in momentum can result in a change in the object's velocity (speed and/or direction of motion) or its state of rest.

Alternative Options:
Let's briefly discuss the other options provided in the question:

a) Change in Momentum: While force does cause a change in momentum, it is not the most accurate definition of force. Force is more specifically defined as the rate of change of momentum, rather than just a change in momentum itself.

c) The Quantity that Opposes Inertia: This definition refers to the concept of inertia, which is the tendency of an object to resist changes in its state of motion. While force does oppose inertia, this definition does not encompass the full meaning of force.

d) The Quantity that Keeps the Velocity Constant: This definition is incorrect. Force is not the quantity that keeps velocity constant. In fact, force is required to change the velocity of an object.

In conclusion, force is defined as the rate of change of momentum. This definition highlights the relationship between force and the change in an object's motion, emphasizing the fact that force is responsible for altering an object's momentum.

The correct ans is option b ....