What is defined as the quantity of radiation that produces one electrostatic unit of electricity in 0.001293 grams of dry air?

The quantity of radiation that produces one electrostatic unit of electricity in 0.001293 grams of dry air is known as the roentgen. The roentgen is a unit measuring exposure to ionizing radiation and is specifically defined based on the ionization of air, making it a crucial measurement in radiography. In this context, the focus is on the capacity of radiation to ionize air and produce measurable electric charge, which is synonymous with the roentgen’s definition.

In contrast, other options such as the coulomb relate to the unit of electric charge, the gray is a unit of absorbed radiation dose, and the electron volt corresponds to energy rather than exposure. Thus, the roentgen is the only unit in the provided options that directly pertains to measuring the exposure by considering the ionization in air, making it the correct choice.