A: The relative acceleration of two objects moving under the effect of gravity, only is always zero, irrespective of direction of motion.
R : The acceleration of object moving under the effect of gravity have acceleration always in downward direction and is independent from size and mass of object

Hint: We know that the acceleration of two bodies under gravity will have zero relative acceleration and hence will be the same irrespective of direction. Using this , find whether the reason matches the assertion or not.

Complete step by step solution:
Given that the relative acceleration of 2 objects under gravity is independent of direction of motion. This statement is true because, if we throw or drop 2 objects in the same force as gravity, the acceleration of the body will be equal. Since the definition of relative acceleration states as difference between the acceleration of body 1 and body 2, and since both are under the influence of gravity, they cancel out each other and produce zero relative acceleration.
Therefore, when there’s zero relative motion between 2 bodies, the bodies are said to be independent of direction of motion.
Now, let us analyze the reason for it. It is given that acceleration of objects moving under the effect of gravity have downward acceleration. This is because, earth’s gravitational force is greater than that of the body, which means that even when a stone is projected with a certain velocity greater than that of gravity, at one point where its velocity becomes lesser than g, the earth’s gravitational pull starts to pull the object down. This applies regardless to a stone or a heavy machine. Which means that it is independent of mass and size.

Thus, both the reason and assertion are true and the reason explains the assertion.

Note:
Escape velocity is a velocity that is used by the object to escape earth’s gravity into space. It is very high and deployed by rockets and spaceships.