Answer
a. Two force pairs act on the apple: Earth’s downward pull on the apple (action 1), and the hand's upward support force on the apple (action 2).
The corresponding reaction forces are: the apple’s upward pull on the Earth (reaction 1), and the apple pushing the hand downward (reaction 2).
b. With no air resistance, one force acts on the apple: Earth’s downward pull on the apple (action 1). The corresponding reaction force is the apple’s upward pull on the Earth (reaction 1).