Newton's second law of motion states that the force acting on a body is directly proportional to the rate of change of its momentum, which is also equal to the product of its mass and acceleration. Thus, the correct statement is that the force acting on a body is directly proportional to the acceleration of the body.

Statics is the branch of mechanics that deals with bodies at rest under the action of forces.

The moment of a force is the rotating or turning effect of a force about a fixed point or fixed axis and is measured by the product of the force and the perpendicular distance between the fixed point or the fixed axis and the line of action of the force. Its formula is τ = F × d.

When a system is in equilibrium, the net force acting on the system is zero. The equilibrant is a force that is equal in magnitude but opposite in direction to the resultant force, such that when the two forces are added together, the net force is zero. Therefore, the correct answer is C)

The resistance of a body to change its state of rest is called inertia of rest.

If the resultant force of all the forces acting on a body is equal to zero, then the body will be in equilibrium. Such forces are called balanced forces.

The unit of force in the SI system of units is newton (N).

A couple is defined as two equal and unlike parallel forces applied simultaneously at two distinct points, which do not produce any translatory motion but cause the rotation of the body. Turning a tap involves two equal and opposite forces applied at different points, which results in the rotation of the tap.