Which term describes a substance that kills rats, insects, and bacteria?

The term that accurately describes a substance capable of killing rats, insects, and bacteria is pesticide. Pesticides are a broad category of chemicals used to control or manage various types of pests, which includes not only insects but also rodents and microorganisms such as bacteria.

Herbicides, while also a type of pesticide, are specifically designed to kill unwanted plants (weeds) and do not target insects or rodents. Insecticides solely focus on insects and therefore would not be effective against rats or bacteria. Fungicides are targeted at fungi and are not intended to kill pests outside of that category. Thus, pesticide encompasses all of these roles, making it the correct term for a substance that functions against a wide range of pests, including rats, insects, and bacteria.