__________ measures how tightly a pesticide sticks to soil particles.

• A. Vaporization coefficient
• B. Tolerance index
• C. Volatility
• D. Adsorption

Answer: (D)

Adsorption is the process by which a pesticide binds to soil particles, especially to surfaces of clay minerals and organic matter. This binding determines how tightly the chemical sticks to the soil and resists being washed away by water. When adsorption is strong, the pesticide stays put in the topsoil, reducing movement to deeper layers and potentially groundwater. This binding is often described by adsorption coefficients (such as Koc), where a higher value means the chemical sticks more firmly to soil. In contrast, volatility describes how readily a substance becomes a gas and moves into the air, and tolerance index relates to how organisms tolerate exposure. So adsorption is the best term for measuring how tightly a pesticide sticks to soil particles.