Alump of putty and a rubber ball have equal mass. both are thrown with equal speed against a wall. the putty sticks to the wall. the ball bounces back at nearly the same speed with which it hit the wall. which object experiences the greater momentum change?

The bouncy ball experiences the greater momentum change.

To understand why, you need to remember that momentum is actually
a vector quantity ... it has a size AND it has a direction too.

The putty and the ball have the same mass, and you throw them
with the same speed.  So, on the way from your hand to the wall,
they both have the same momentum.
Call it " M in the direction toward the wall ".

After they both hit the wall:

-- The putty has zero momentum.
    Its momentum changed by an amount of  M .

-- The ball has momentum of " M in the direction away from the wall ".
    Its momentum changed by an amount of  2M .