Absence of air in soil limits the activity of:

Correct option is C

The absence of air, or oxygen, in the soil significantly limits the activity of microorganisms, particularly aerobic organisms that require oxygen for respiration. It also affects the oxidation processes in the soil, which are critical for nutrient cycling, organic matter decomposition, and maintaining soil health. Under anaerobic conditions, different microbial communities take over, and processes like denitrification may occur, which reduces soil fertility.