Answer:
The ball slows down in the air due to an unbalanced force.
Step-by-step explanation:
As we know that the unbalanced forces on an object will accelerate it or decelerate it from its initial speed
So here we know that

now if the speed of the ball is decreasing and it come to rest then we must say that the motion of the ball is accelerated motion in which its speed is slowing down
So here the force on the ball must be unbalanced force due to which its motion must be accelerated
So correct answer will be
The ball slows down in the air due to an unbalanced force.