Consider the following organisms:

Correct Option (B):

Nostoc is a genus of cyanobacteria, also known as blue-green algae. It possesses the capability to fix atmospheric nitrogen into a usable form for plants. This nitrogen-fixing ability makes Nostoc an effective biofertilizer, particularly in paddy fields, where it enhances soil fertility and contributes to increased crop yields.

Incorrect Options:

Agaricus is a genus of saprophytic fungi, commonly known as mushrooms. It does not possess nitrogen-fixing capabilities or other properties that would qualify it as a biofertilizer.

Spirogyra is a type of filamentous green alga. Unlike certain cyanobacteria, Spirogyra does not have the ability to fix atmospheric nitrogen. Therefore, it is not utilized as a biofertilizer.