Question

give an example when acceleration is against the direction of motion.

does velocity of a body remain constant during free fall ?why or why not.

Answer 1

When we throw a ball up in the air, the acceleration is downwards but the ball is moving upwards because it has some initial velocity. It will continue moving up untill it reaches zero velocity.
Velocity of body increases during free fall because there is a contant acceleration g acting on the body. So if we neglect air drag, the body will fall with increasing velocity.