The correct answer is (c) Azolla.
Azolla is a small, free-floating fern that grows in freshwater. It is a popular biofertilizer because it can fix nitrogen from the air, which is essential for plant growth. Azolla is also a good source of protein and other nutrients for fish and other aquatic animals.
Yeast is a single-celled fungus that is used in baking, brewing, and winemaking. It is not a source of biofertilizer.
Chlorella is a green algae that is used as a food supplement and a source of biofuel. It is not a source of biofertilizer.
Mold is a fungus that can grow on food, wood, and other organic materials. It is not a source of biofertilizer.
Here is a table that summarizes the information about each option:
| Option | Description | Is a source of biofertilizer? |
|—|—|—|
| Yeast | A single-celled fungus that is used in baking, brewing, and winemaking. | No |
| Chlorella | A green algae that is used as a food supplement and a source of biofuel. | No |
| Azolla | A small, free-floating fern that grows in freshwater. It is a popular biofertilizer because it can fix nitrogen from the air, which is essential for plant growth. | Yes |
| Mold | A fungus that can grow on food, wood, and other organic materials. | No |