Question

A book rests on a table. The earth pulls down on the book through the weight force. Which force is the reaction force to the weight force?
1. the force of the Earth on the book
2. the force on the table on the book
3. the force of the Earth on the table
4. the force of the book on the Earth
5. the inertia of the book

Answer 1

Newton's 3rd law: The force that A exerts on B is equal and opposite (in direction) to the force that B exerts on A.

Substitute the words "the earth" for A and "the book" for B.