Which tool is specifically designed to remove and replace small screws in various appliances?

The screwdriver is specifically designed to remove and replace small screws in various appliances, making it the appropriate tool for this task. A screwdriver features a handle and a shaft with a tip that fits into the head of a screw, allowing for precise turning to either fasten or loosen screws without damaging them. This tool is essential in appliance repair as it allows technicians to access and service parts that are secured with screws, which are commonly found in many appliances.

Other tools mentioned, such as pliers, are primarily designed for gripping and twisting, but they do not provide the same level of control and precision for screw manipulation. A knife could potentially be used for various cutting tasks but is not designed for engaging screws. Lastly, a hacksaw is mainly used for cutting through materials like metal or plastic and is not suitable for handling screws. Therefore, the screwdriver is the most effective and appropriate tool for the specific task of removing and replacing small screws in appliances.