Harry has two types of materials of the same mass, one is a piece of paper, the other a copper ball. (a) explain why the copper ball hits the ground first when both are dropped near the surface of the earth even if they experience the same gravitational acceleration.

In order to fall, both objects have to push the air out of their way so they can get by.  The copper ball is smaller, smoother, spherical, and streamlined.  The paper is bigger, rougher, flat, and a shape that doesn't slip and slide through anything too easily.  The force of air resistance, acting opposite to gravity and trying to hold the falling object up, is greater on the paper than on the copper ball.

If you could drop them in a place with no air, like in a vacuum chamber or on the Moon, they would hit the ground at the same time.

One of the Apollo astronauts ... I don't remember which one or which mission ... while he was on live video from the moon, took a feather and a hammer and dropped them at the same time.  Sure enough, they both hit the ground at the same time.