Which of the following units would be most relevant for calculating exposure to ionizing radiation in air?

In the context of calculating exposure to ionizing radiation in air, the most relevant unit is Air Kerma. Air Kerma essentially measures the kinetic energy released in air per unit mass due to ionizing radiation and is particularly useful for quantifying the exposure level of ionizing radiation in air.

This measurement takes into account the radiation's ability to produce ionization in air, making it directly applicable for assessing how much radiation air is absorbing, which is crucial for evaluating exposure risks.

While other units like Gray, Sievert, and Becquerel play important roles in radiation measurement—Gray quantifies absorbed dose, Sievert relates to biological effect, and Becquerel measures radioactivity—they are not specifically designed to assess exposure in air as directly as Air Kerma does. The focus on kinetic energy transfer in air makes Air Kerma the appropriate choice for this scenario.