Give scientific reason:
When an object falls freely to the ground, its acceleration is uniform.

Hint: When an object falls freely on the ground, the force of the gravity works on it. So the acceleration on the object is the acceleration due to gravity. So the acceleration is uniform on the freely falling body.
Formula Used:
In this question we will be using the following formula,
$F = ma$ where $F$ is the force acting on the body and $m$ is the mass of the body and $a$ is the acceleration.
and $F = G\dfrac{{Mm}}{{{R^2}}}$
where $G$ is the universal gravitational constant.
$M$ is the mass of the earth and $R$ is the radius of the earth.

Complete answer:
When a body is taken to a height and then dropped, then the body is pulled towards the surface of the earth. This force is the force of gravity of the earth pulling the body towards its surface. So we see that the body falls freely.
The force of gravity of the earth is given by the formula,
$F = G\dfrac{{Mm}}{{{R^2}}}$
So this is the force that causes the acceleration of the body in the downwards direction.
Let us consider the acceleration of the body is $a$.
So the force on the freely falling body is,
$F = ma$
So we can equate these two forces and hence get.
$ma = G\dfrac{{Mm}}{{{R^2}}}$
Therefore, we can cancel the mass of the body $m$ from both sides of the equation, and we get
$a = \dfrac{{GM}}{{{R^2}}}$
Hence we can see that the acceleration depends on the gravitational constant $G$, the mass of earth $M$ and the radius of earth $R$. Since all of these values remain constant so the acceleration of the freely falling body will remain constant.

Note:
This acceleration which we derived $a = \dfrac{{GM}}{{{R^2}}}$ is generally denoted by the letter $g$ and termed as the acceleration due to gravity. As this value is independent of the mass of the body, so in the absence of any other kind of force, the acceleration is constant for all bodies irrespective of their masses.