The force of Earth's gravity pulls down on a stone after someone tosses it off a cliff. What is the "equal and opposite force" during this interaction, according to Newton's third law?

The equal and opposite force is the force of the stone's gravity pulling up on thy Earth.

Explanation:

                                     

When someone tosses a stone off a cliff, the force of gravity of Earth pulls down and the force of the stone's gravity pulls up on the Earth due to the equal and opposite reaction exerted between the Earth and the stone.In Newton's third law, two important features are present. One is the force exerted on two bodies will have the same magnitude but opposite direction. The other feature is force is acting on two different objects.This exerted force is equal in magnitude but opposite in direction whereas the gravity exerts a downward force on a stone and upward force on an Earth which is opposite in direction.