Question

a ball is tossed vertically upward rises, reaches it's highest point, and then falls back to its starting point. during the time, the acceleration of the ball always?

Answer 1

Aside from any outside forces or friction or air resistance, the ball's acceleration remains constant between the ball leaving the hand and hitting the ground.
Hope this helps!

Answer 2

Ignoring the effects of air resistance, the acceleration of the ball is
constant once it leaves the thrower's hand.

It is the acceleration of gravity on Earth . . . 9.8 m/s² downward, from
the moment the ball is released until it hits the ground.