Now the body is at point C, just before touching the ground. So, height from ground is 0.

Potential energy at point C is P.E. = 0 [height = 0]

Velocity of body at point C is v_{C} then, v_{C}^{2} = u^{2} + 2as = 2gh [as u = 0, a = g and displacement of body from A is h]

Kinetic energy of body at point C is K.E. = mv_{C}^{2} = m2gh = mgh

Total energy of body at point C is T.E. = P.E. + K.E. = 0 + mgx = mgh

Therefore total energy remain same at all points on the freely falling motion of a body. So, mechanical energy is conserved.