What will happen if- (a) Microbes in the soil get destroyed.

Hint: Soil composed of many microorganisms, which have both advantage and disadvantages, where microorganisms include bacteria, protozoans, Archaebacteria, fungi, different variety types which makes the soil nutrient rich and makes it fertile for the plants or crops growth.

Complete answer:
> Microorganisms play an important role for soil fertility, and there are a variety of microorganisms that are found on the earth and the study of microorganisms in the soil is called soil biology.

> Microorganism play very important role in nutrient cycling where some organisms in the soil associates with the plants and involves in the nitrogen fixation where it converts the atmospheric nitrogen to ammonia and then to nitrates and nitrites which makes the soil nutrient rich with nitrogen that is very important for plant growth.

> Some mycorrhizae of fungi they feed on dead and decaying organisms and other dead organic matter and makes the soil nutrient rich, and it increases the availability of the mineral nutrients, and it improves the fertility status.

> At the same time soil microbes create humus that makes the soil more suitable for plant growth. Some microbes solubilize the Phosphorus which makes it more available in the soil makes the soil phosphorus rich that helps in plant growth

> Microorganisms also improve the structure of the soil, which makes soil free from erosion.
So if the microbes in the soil get destroyed it effects the soil respiration and Also the nutrient cycling that makes soil more dumb and it becomes useless for the plant growth. So the destruction of microorganisms in the soil disturbs the whole harmony that has with soil and plants and association with the environment makes Soil less nutritious.

Hence, the correct answer is option (B).

Note: Soil is the home for many microorganisms which makes soil more rich in nutrients by various mechanisms and also makes the soil more porous and helps for the passage of air and all, at the same time some microorganisms in the soil are pathogenic may destroy the plants by causing certain disease.