Answer:
The change in momentum of the ball is 24 kg-m/s
Explanation:
It is given that,
Mass of the ball, m = 1 kg
Initial velocity of the ball, u = -12 m/s (in downwards)
Final velocity of the ball, v = +12 m/s (in upward)
We need to find the change in momentum of the ball.
Initial momentum of the ball, 
Final momentum of the ball, 
Change in momentum of the ball, 

So, the change in momentum of the ball is 24 kg-m/s. Hence, this is the required solution.