The rate of change of momentum is equal to the:

• According to Newton's second law of motion, the rate of change of momentum is equal to the applied force. 
• Force
  $\left(F\right)=\frac{\Delta P}{\Delta t}$    ----(1)
  Where $\Delta \mathrm{P}=$ Change in momentum and $\Delta t=$ change in time taken.
  Momentum (P): The product of mass and velocity is called momentum.
  Momentum $\left(P\right)=mass\left(m\right)\times$ Velocity $\left(\mathrm{v}\right)$
• Equation (1) can be further simplified as:
• $\left(F\right)=m\frac{\Delta v}{\Delta t}$, mass is constant
• We know that rate of change of velocity per unit of time is defined as acceleration, therefore, the force can also be expressed as:
• F = m a

Therefore, force is the correct answer.