Which of the following is a risk factor in using the trailer hand valve during motion?

Using the trailer hand valve during motion can indeed create a hazardous skid, making this the correct answer. The trailer hand valve is designed to control the trailer’s brakes independently from the tractor's brakes. When applied while the vehicle is in motion, particularly during turns or at high speeds, it can cause the trailer wheels to lock up. This locking can lead to a loss of traction, resulting in the back end of the trailer swinging out, which creates a skidding scenario. Such skids can be difficult to manage and can significantly increase the risk of accidents.

Meanwhile, while immediate braking and increased tire wear may be concerns in certain contexts, they do not specifically pertain to the risks associated with using the hand valve during motion in the same way that a skid does. Stabilizing the trailer is not a function of the hand valve when the vehicle is in motion; rather, it can destabilize it if not used carefully. Thus, the emphasis on the risk of skidding captures the primary danger associated with this practice.