Newton's Third Law of Motion

Newton's Third Law states that whenever one object exerts a force on a second object, the second object exerts an equal and opposite force back on the first.

The crucial detail is that the reaction force acts on a different object — never the same one. Forces acting on the same object can cancel; forces on different objects cannot.

The first option correctly identifies both 'equal and opposite' AND 'on a different object', making it the complete and accurate statement of Newton's Third Law.

The choice “For every action force, there is an equal and opposite reaction force acting on the same object.” says the reaction force acts on the 'same object' — this is the most common misconception. If both forces acted on the same object, they would cancel and nothing would ever move. Eliminate.

The choice “A net force causes an object to accelerate in the direction of that force.” describes Newton's Second Law ($F=ma$), not the Third Law. Eliminate.

The choice “An object at rest remains at rest unless acted upon by a net force.” describes Newton's First Law (inertia). Eliminate.

The choice “For every action force, there is an equal and opposite reaction force acting on a different object.” is the only statement that correctly describes action-reaction force pairs acting on different objects — the defining feature of Newton's Third Law.

A true action-reaction pair must: (1) act on two different objects, (2) be equal in magnitude, (3) be opposite in direction, (4) be the same type of force, and (5) occur simultaneously.

Earth exerts a gravitational force downward on the book; the book exerts a gravitational force upward on Earth. These act on different objects (Earth and book), are the same type (gravitational), equal in magnitude, and opposite in direction. ✓

The gravitational force from Earth on the book and the normal force from the table on the book both act on the same object (the book) and are different types of force (gravitational vs. contact). This fails two criteria — not a Newton's Third Law pair.

Only The choice “The gravitational force of Earth on the book (downward) and the gravitational force of the book on Earth (upward).” satisfies all criteria for a Newton's Third Law pair.

Both forces in The choice “The gravitational force of Earth on the book (downward) and the normal force of the table on the book (upward).” (gravity from Earth and normal from table) act on the same object — the book. Newton's Third Law pairs always act on different objects. Eliminate.

This pair involves the table exerting forces on two different objects (book and floor), not a mutual interaction between two specific objects. Not a valid Newton's Third Law pair. Eliminate.

Both forces described point downward — a Newton's Third Law pair must be opposite in direction. Also, weight and normal force from book on table are different types. Eliminate.

The choice “The gravitational force of Earth on the book (downward) and the gravitational force of the book on Earth (upward).” describes two gravitational forces — same type, opposite direction, acting on different objects (book and Earth). This is the correct Newton's Third Law pair.