Which of the following baking tools is least energy-efficient?

The electric mixer is considered the least energy-efficient baking tool among the options provided. This is primarily because electric mixers typically use a significant amount of electricity for relatively short periods to mix ingredients thoroughly. While mixing is essential, it doesn't contribute directly to cooking or baking food, which is where most energy consumption and efficiency are considered.

In comparison, an oven, while consuming more energy overall for baking, is designed for cooking larger quantities of food evenly and can often be used for multiple dishes at once. A slow cooker utilizes low heat over an extended period, making it quite energy-efficient for preparing meals that require long cooking times. Similarly, a toaster oven uses less energy than a conventional oven due to its smaller size, enabling it to preheat and cook food more quickly.

The energy consumption of a tool is not just based on its power rating, but also on how effectively it uses that energy to achieve the desired outcome. In this case, the electric mixer, while effective for its purpose, does not directly contribute to the cooking process and therefore ranks lower in overall energy efficiency when compared to the other culinary appliances listed.