Question

for a planet orbiting the sun in a circular orbit give the magnitude of the torque acting on the planet due to the gravitational force exerted on it by the sun give reason for your answer​

Answer 1

If the planet is moving with a constant velocity in a purely circular orbit, then the torque due to  the gravitational force exerted on it by the sun will be zero.

Explanation :

If the planet is moving along the circular path with uniform speed, it will have a radial acceleration resulting in a radial force, hence the Torque, which is the cross product of Radial vector and Force will be zero since angle between both is zero.