Which of the following is an example of a biofertilizer?

Cyanobacteria

The correct answer is: (c) Cyanobacteria

Explanation: A biofertilizer is an organic substance that contains living microorganisms, such as bacteria, fungi, or cyanobacteria, which help in enhancing the nutrient quality of the soil and promote plant growth.

Unlike common salt (a), synthetic fertilizer (b), and insecticide (d), which are chemical substances, cyanobacteria are natural microorganisms that can fix atmospheric nitrogen and convert it into organic compounds, making them beneficial as a biofertilizer.

Cyanobacteria, such as Anabaena, Nostoc, and Oscillatoria, play a significant role in increasing soil fertility and supporting plant growth, particularly in paddy fields and other agricultural environments.