Question

The contact force exerted by a body A on another body B is equal to the normal force between the bodies. We conclude that
(a) the surfaces must be friction-less
(b) the force of friction between the bodies is zero
(c) the magnitude of normal force equals that of friction
(d) the bodies may be rough but they don't slip on each other.

Answer 1

Answer ⇒ Option (b). and Option (d).

Explanation ⇒  For the contact force to be equal to the normal force, the surface need not to be frictionless.

But the force of friction between the bodies must be zero for the N to be equal to F.

This also tells that the the surface may be rough but they are not slipping on each other, I means that Friction is zero. Thus, Option (b). and (d). both may be correct.

For the contact force to be equal to the normal force, friction for the surface should not need to be zero.  If the magnitude of the Normal force will be equal to the contact force this means that body is at rest.  

Thus, Both the options (a). and (c). are not correct.

Hope it helps .