Question

show that the gravitational torque about Centre of mass is zero​

Answer 1

Answer:

It is not necessary that the gravitational torque at the centre of mass is zero.

The centre of gravity is the point where gravitational torque is zero.

Only if the centre of mass of the body coincides with the centre of gravity of the body, will the gravitational torque be zero ( at the centre of mass ).

Hope it helps ^_^