The region labelled 6 refers to the bacteria convert nitrogen gas into compounds usable by living things.
Nitrogen cycle
The nitrogen cycle refers to the movement of nitrogen through nature. It is one of the biogeochemical cycles that exists in nature. Nitrogen is very important to living things.
In the diagram, the region labelled 6 refers to the bacteria convert nitrogen gas into compounds usable by living things. The process is called nitrification.
Learn more about the nitrogen cycle: https://brainly.com/question/9243222