An object of mass m rests on a flat table. The earth pulls on this object with a force of magnitude mg. What is the reaction force to this pull?

The reaction force of the object on the flat table will be in upward direction with the same magnitude mg.

Explanation:

According to third law of motion, every action has equal and opposite reactions. So here, the action is the gravitational pull acting downward on the object kept on table with a magnitude of mg.

So as per third law, the reaction of the object will be in opposite direction to the action i. e., the pull will be in the upward direction as reaction to the gravitational pull toward downward direction and the magnitude should be same as mg.

Thus, the reaction exerted by the object on the table for the action of gravitational force of magnitude will be the upward pull of the object from the table with the magnitude mg and as both the action and reaction will be canceling each other, the object will remain at the same position on the table without any motion as there is no unbalanced force in the system.

Take into account Newton's 3rd Law. The reaction force would be the object pulling upward on the Earth with a force 'mg'.