Which simple machine is characterized by rotating about an axle that serves as a fulcrum?

The wheel and axle is a simple machine that operates by rotating around a central axle, which functions as a fulcrum. This design allows for the reduction of friction and enhances the efficiency of moving or lifting loads. The wheel's larger diameter compared to the axle means that turning the wheel results in a greater mechanical advantage, allowing a smaller force applied to the wheel to lift or move a heavier load attached to the axle.

In contrast, other options reflect different mechanics: a lever pivots around a fulcrum but does not involve a rotating mechanism like the wheel and axle. A pulley employs a rope and a grooved wheel to change the direction of a force but not around an axle in the sense described here. An inclined plane is a flat surface tilted at an angle, facilitating easier movement of objects upward but without any rotation involved.

Thus, the characteristics of the wheel and axle best fit the description provided in the question, making it the correct answer.