Air Kerma is expressed in units of which of the following?

Air Kerma is correctly expressed in units of Gray (Gy). The term "Kerma" stands for Kinetic Energy Released in Matter, and it specifically quantifies the energy transferred from photons (such as X-rays or gamma rays) to charged particles (typically electrons) in a given mass of air. The Gray is defined as the absorption of one joule of energy per kilogram of the absorbing substance. Since Air Kerma is related to energy deposition in a specific medium (air, in this case), it is appropriate to use Gray as the unit of measurement.

The other units mentioned do not relate directly to the measurement of Air Kerma. Sievert is a unit used for measuring the biological effect of ionizing radiation, while Rem is a legacy unit that also measures radiation's biological impact but is less commonly used today. Curie, on the other hand, is a unit used to express radioactivity levels and does not address the energy transferred to matter; therefore, it does not apply to the context of Air Kerma.