Why is the anode of the X-ray tube rotated?

The rotation of the anode in an X-ray tube is primarily done to increase the heat capacity of the anode. When the anode rotates, it allows for a larger surface area to be exposed to the electron beam at any given moment. This distribution of the heat generated when the electrons hit the anode prevents any one spot from overheating, which enables the tube to handle the extreme heat produced during X-ray generation.

A stationary anode would quickly become too hot, risking damage to the tube and affecting its performance. By using a rotating anode, the heat is spread out over a greater area and is dissipated more efficiently, thus allowing the X-ray tube to function effectively over longer periods and with higher exposure settings.

While the other choices may relate to aspects of X-ray operation, they do not directly correlate with the fundamental reason for the rotation of the anode.