Assertion Even though net external force on a body is zero, momentum need not to conserved.Reason The internal interaction between particles of a body cancels out momentum of each other.       [AIIMS 2019]

By Newton's second law of motion, net external force applied on a system is equal to rate of change of momentum.i.e.  Fext = dpdt If Fext = 0, then dpdt = 0 ⇒ p = constanti.e. When Fext = 0, then momentum of the system remains conserved.The internal interaction between particles of a body do not contribute to change in total momentum of body.Hence, both Assertion and Reason are false.