What property of a chemical determines its volatility?

The property that determines a chemical's volatility is vapor pressure. Volatility refers to how readily a substance can vaporize; this is directly related to its vapor pressure. A substance with high vapor pressure at a given temperature will more readily enter the gas phase, indicating high volatility, while a substance with low vapor pressure will not vaporize easily.

Vapor pressure is influenced by temperature and intermolecular forces within a substance. When these intermolecular forces are weaker, the vapor pressure increases, meaning that the substance is more volatile. Conversely, if the intermolecular forces are stronger, the vapor pressure is lower, corresponding to a less volatile substance. This relationship is crucial for understanding how chemicals behave in various environments, particularly in pest management applications where the volatility of active ingredients can affect their efficacy and distribution.

The other options do not directly determine volatility. Viscosity relates to a substance's resistance to flow, density is a measure of mass per unit volume, and pH levels indicate the acidity or basicity of a solution—all of which are important properties but do not define a chemical's ability to vaporize.