Final answer:
Drills are the most varied category of rotary instruments, available in many forms, and capable of being equipped with a wide range of bits for different purposes.
Step-by-step explanation:
The question you've asked is regarding which category of rotary instruments is the most varied. The answer is c) Drills. Drills are arguably the most varied category of rotary instruments because they come in many forms and can be equipped with a multitude of different bits for various tasks.
For example, a power drill is versatile and can be used in many situations, readily accepting an array of bits for drilling holes, driving screws, and more. Furthermore, specialized drills for construction, woodworking, metalworking, and even healthcare (such as dental drills) show the wide range and adaptability of these tools.
Even though socket wrenches and power drills are great tools, it's the drills that offer greater variation in their use cases. Socket wrenches are specifically designed for applying torque to fasteners, usually nuts and bolts. As depicted in Figure 2.31, a wrench can provide grip and mechanical advantage in applying torque to turn a nut.
The process is straightforward: you turn counterclockwise to loosen the nut and clockwise to tighten it. Hammer, being primarily a tool for impact, is less varied in function compared to drills.