ANS:C - the same as the depression of the liquid at the axis of rotation

When we say "the same as the depression of the liquid at the axis of rotation," we are referring to the concept that the depression of the liquid at the axis of rotation is equal in magnitude to the rise of the liquid along the walls of a revolving cylinder. In a rotating cylinder, due to centrifugal forces, the liquid experiences an outward force. This force causes the liquid to move away from the axis of rotation and rise along the walls of the cylinder. As a result, a concave meniscus forms along the walls, and the liquid level is higher than it would be if the cylinder were not rotating. At the axis of rotation, the centrifugal force is minimal or zero. Therefore, the liquid tends to move towards the center, causing a depression at the axis of rotation. The depression at the axis of rotation is essentially the opposite of the rise along the walls. So, the statement "the same as the depression of the liquid at the axis of rotation" implies that the magnitude of the rise of the liquid along the walls is equal to the magnitude of the depression at the axis of rotation, resulting in a balanced system. This phenomenon is observed in rotating cylinders and is important in understanding fluid behavior under centrifugal forces.