The correct answer is the following.
The forces that act on the piano are: 2) gravitational force acting on the piano (piano's weight). 5) force of the floor on the piano (normal force). 7) force of Chadwick on the piano.
As we see in the picture that I have attached is Chadwick pushing the piano in a horizontal plane. So Chadwick is applying a force that produces an acceleration. It is his force on the piano plus the acceleration of the weight of the piano, it's a gravitational force. This is pure physics applied to an object.
