Final answer:
An axis (Option B) is the correct term for the shaft around which a wheel rotates. It's the central line that allows the wheel to turn in a wheel and axle system, which functions as a lever and force multiplier.
Step-by-step explanation:
The term used to describe the shaft around which a wheel rotates is most accurately defined as the axis (Option B). An axis is an imaginary line about which an object rotates. In the case of a wheel and axle system, the axle serves as the physical manifestation of this axis. Wheels, like those on a wheelbarrow, rotate around the central axle, which is not considered the fulcrum. Instead, the fulcrum is the point about which a lever rotates, which is different from the wheel and axle mechanism. In mechanical terms, the axle is a type of lever with the fulcrum at its center, allowing for rotational motion of the wheel about it. The physics of their action involve concepts such as moment of inertia and torque, with the wheel and axle being a form of lever where force applied on the wheel translates into greater force on the axle, hence acting as a force multiplier.