When sitting at rest in a chair, the "action force" is the force of gravity is pulling you down.

Question

The "reaction force" is the Normal Force which:

Acts in the SAME direction and also pulls you down

Acts in the OPPOSITE direction and pushes back up against you

Answer 1

The "reaction force" is the Normal Force, which:

Acts in the OPPOSITE direction and pushes back up against you.

When you sit in a chair, the force of gravity pulls you down (the action force), and the Normal Force exerted by the chair acts in the opposite direction, pushing you back up to support your weight. This pair of forces illustrates Newton's third law of motion, which states that for every action, there is an equal and opposite reaction.