A handball falls on the ground and rebounds elastically along the same line of motion. Then
a)	The linear momentum of the universe remains conserved
b)	The linear momentum of the ball is not conserved
c)	During the collision, the whole of the kinetic energy of the ball is converted into potential energy and then completely converted into kinetic energy of the ball
d)	During the collision, the kinetic energy remains constant

(a,b,c)

When the ball collides with the ground elastically, then a force is exerted by the ground on the ball along the vertical upward direction. An equal but opposite reaction is offered by the ball on the ground. Therefore, there is no resultant force on the system of ball and ground. Hence, the momentum of universe remains constant. Hence, option (a) is correct.

Since during collision, a force is exerted by the ground on the ball, therefore due to this impulsive reaction, momentum of the ball gets changed

If the ball collides with the ground with velocity , then change in momentum of the ball is equal to  and this change takes place along vertically upward direction. Hence momentum of the ball does not remain conserved. Therefore, option (b) is correctDuring the collision, at an instant, centre of mass of the ball comes to rest. At that instant the ball has the maximum deformation. Due to that deformation, the ball tries to regain its original shape. Hence, it gets rebound. Hence, at an instant, during the collision, the whole of KE gets converted into its deformation energy which ultimately converts into KE. Therefore, option (c) is correct