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**Hint:**We should know that freefall is a special case of motion with constant acceleration, because acceleration due to gravity is always constant and downward. This is true even when an object is thrown upward or has zero velocity. Acceleration from gravity is always constant and downward, but the direction and magnitude of velocity change. According to our principle, when an object is slowing down, the acceleration is in the opposite direction as the velocity. Thus, this object has a negative acceleration.

**Complete step-by step answer:**

We should keep in mind that since g is calculated using only constants, g is a constant. where Re is the radius of the earth. As earth is not a perfect sphere, the value of gravity g is not a constant at all the locations on the surface of the earth. Therefore, for practical purposes we take acceleration due to gravity as a constant.

We should be knowing that the acceleration due to gravity is always negative. Any object affected only by gravity (a projectile or an object in free fall) has an acceleration of $-9.81m/{{s}^{2}}$, regardless of the direction. The acceleration is negative when going up because the speed is decreasing.

It is seen that the first the assertion says that acceleration due to gravity does not depend on mass of the body it is true as because if we drop an egg and a watermelon from same height at same time both will hit the ground at the same time so Assertion is true but the reason acceleration, due to gravity is constant quantity is false because gravitational force depends on a separation which is not constant.

**Hence, the correct answer is Option C.**

**Note:**It should be known to us that acceleration is the rate of change of velocity with time. As the velocity is a constant value over all the values of time, the rate of change of velocity is thus zero. So, acceleration is zero. So, zero acceleration and non-zero velocity are possible for particles moving with constant velocity. In the case of the earth, the force of gravity is greatest on its surface and gradually decreases as you move away from its centre as a square of the distance between the object and the centre of the Earth. Of course, the earth is not a uniform sphere so the gravitational field around it is not uniform.

On the other hand, the sensation of weightlessness, or zero gravity, happens when the effects of gravity are not felt. Technically speaking, gravity does exist everywhere in the universe because it is defined as the force that attracts two bodies to each other. But astronauts in space usually do not feel its effects.

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