Before going to answer this question first we have to understand Newton's third law.
As per newtons third law ,for every action,there is an equal and opposite reaction.The force exerted by a body on other body is called action and force that the body gets in turn is called reaction. They will always act on two different bodies and their direction will be opposite to each other.
As per the question a object is falling under gravity. We are asked to find out the action and reaction forces.
We know that every object having mass will imparts gravitational forces on each other.In this question the earth will apply the force of gravity on the body which is in vertically downward direction.Due to this gravity,the body will fall towards earth with an acceleration of 9.8 m/s^2 .This is the force of action.
The falling object also applies same amount of force on earth in vertically upward direction.But we will not notice any acceleration of earth.It is so because the earth is very massive, so the acceleration produced by earth is very small.The force exerted by the falling object on earth is the force of reaction.
