Assertion (A): Soil clay has maximum influence on soil behavior.
Reason (R): Clay has a greater surface area per unit mass and is most physiochemically active.

Correct option is A

Clay particles have a very high surface area relative to their mass, making them highly active in chemical and physical soil processes. This property gives clay a dominant influence on soil behavior such as water retention, nutrient holding, and cation exchange capacity. Hence, both A and R are true, and R correctly explains A.