Among the options you've provided, Disinfecting is the term that specifically refers to the process of killing or inactivating infectious agents.
Here's a brief overview of the other terms:
- Sanitizing: Reduces the number of germs to a safe level, but does not necessarily kill all infectious agents.
- Immunizing: Involves stimulating the immune system to protect against infectious agents but does not kill them directly.
- Purifying: Generally refers to removing contaminants, which may include pathogens, but doesn’t specifically imply killing them.
So, the correct answer is Disinfecting.