Protozoans are the only organisms that can convert nitrogen from the air into chemical compounds that plants can use.
a. true
b. false

False

Explanation:

Protozoans are not the organism that fix nitrogen for the plants. The organism that fix nitrogen to convert it into a form which can be used by plants are known as diazotrophs.

These are bacteria and archae that fix nitrogen gas found in the atmosphere into more usable form such as ammonia.

These organism can grow without any external source of fixed nitrogen. Example: Rhizobia and azospirillium.

c. is the correct answer