$A$ couple produces

Which factors should be considered for the calculation of torque,and which should not?

$A$ force $\vec{F} = 4\hat{i} + 3\hat{j} + 4\hat{k}$ is applied at the intersection point of the plane $x = 2$ and the $x$-axis. The magnitude of the torque of this force about the point $(2, 3, 4)$ is .......... . (Round off to the nearest integer)

For a particle moving in a circular path under the influence of a central force,the angular momentum remains constant because .......

The rotational effect is produced by

The torque acting on a body about the centre of mass due to the normal reaction: