Question

Azolla is used as a biofertilizer as it has
(a)Rhizobium
(b)Cyanobacteria
(c)Mycorrhiza
(d)Large quantity of humus

Answer 1

A substance that consists of living microorganisms and helps in promoting the growth of the plant by increasing the supply or availability of the primary nutrients are biofertilizers.

Complete answer:
Azolla consists of cyanobacteria which are used as a biofertilizer. The leaves of Azolla consist of cyanobacteria which are algae and consist of the enzyme nitrogenase in the heterocyst which is specialized cells in the algae. They help in the fixation of nitrogen in the cells with the help of the enzyme nitrogenase and increases the yield. The cyanobacteria produce a range of toxins which are dangerous for the human and animals are known as cyanotoxins. It contributes nitrogen up to 60 kg and enriches the soil with organic matter. Biofertilizers help in fixing the nutrient availability in the soil and symbiotically gets associated with the plant roots and are involved in safely converting complex organic materials into the simpler compounds which are easily taken up by the plants. they produce a large number of crops with the ability to fix nitrogen and phosphorus that solubilize the greatest possible effect. They promote healthy soils and lead to the greater farming system and ability and advance the shoot and root growth of many crops which is important when implementing new seed growth.

Additional information:
Rhizobium: It is a diazotrophic bacteria which helps in the fixation of nitrogen in the root nodules of legumes. deer found in the soils and is a group of soil bacteria that produces nodules in the legume and fixes nitrogen gas from the atmosphere which turns into a useful form of nitrogen. The nodules break down and release the rhizobium back into the soil when the legume dies and lives individually or reinfects a new legume host.
Mycorrhiza: They are a symbiotic association of a fungus and a plant that play important role in soil biology, plant nutrition, and soil chemistry. This association is sometimes mutualistic and the fungus colonizes the host plant's root tissues. The association with mycorrhizal fungi is founded to hoard nitrogen from the root of the plants in times of nitrogen scarcity.
A large quantity of humus: The organic material which forms in the soil by dead plant and animal matter is humus. It is produced naturally or by composting which is the collection of organic material such as food and garden scraps which turns out into the soil.

So, the correct answer is 'Cyanobacteria'.

Note: Azolla is a freshwater phone which is located in certain regions of Western Europe, Southern Africa and New Zealand. They flow slowly in the streams and rivers where there are tropical climatic conditions with minimum water temperature that remains above zero degree celsius throughout the year.