Assertion (A) : On a wet floor of a bathroom, a small circular area around a pinch of foam appears to be dry. Reason (R) : Soap molecules reduce surface tension and increase surface area of the thin layer of water on the wet floor.

The correct answer is Option 1.

The Assertion (A) is true because when soap or foam is introduced to a thin film of water on a floor, the water appears to recede from the soap, leaving a seemingly dry circular patch. This phenomenon is driven by the principles of surface tension explained in the Reason (R).

Soap acts as a surfactant, significantly reducing the surface tension of the water at the point of contact. The surrounding water, which has higher surface tension, exerts a stronger outward pull on the soapy water. This differential in surface tension (the Marangoni effect) causes the water to be drawn away from the foam. As the water moves outward, it spreads over a larger surrounding region, effectively increasing the surface area of that thin layer while leaving the central area around the foam depleted of water, or "dry." Thus, R correctly explains the mechanism behind A.