Which unit would be used to describe radiation exposure in air?

Coulombs per kilogram is the correct unit to describe radiation exposure in air because it measures the amount of electrical charge produced by ionizing radiation in a specific volume of air. This unit is essential in understanding the interaction of radiation with air, as it quantifies the ionization produced. This allows for a standardized means to calculate exposure levels, which is crucial for ensuring safety in environments where radiation is present.

Other units listed, such as Gray, Rad, and Rem, are used for different contexts in radiation measurements. Gray and Rad are units of absorbed dose and are used to measure the energy deposited in a material by radiation. The Rem is a unit that accounts for the biological effect of radiation by incorporating a quality factor, making it suitable for dose equivalent calculations rather than exposure. Thus, for specifically measuring exposure in air, coulombs per kilogram is the appropriate unit.