What is defined as radiation that has enough energy to ionize atoms or molecules?

Ionizing radiation is defined as radiation that possesses enough energy to remove tightly bound electrons from atoms or molecules, thus creating ions. This process of ionization can lead to significant changes in chemical properties and can have biological effects on living tissues, making it a crucial concept in radiation safety and health physics.

In contrast, non-ionizing radiation does not have enough energy to ionize atoms or molecules. It includes types of radiation like radio waves and visible light, which primarily cause heating effects rather than ionization. Thermal radiation, typically associated with heat transfer, involves the emission of energy by all matter with a temperature above absolute zero and doesn’t necessarily involve ionization. Electromagnetic radiation encompasses a wide spectrum, including both ionizing and non-ionizing radiation, but does not specifically pertain to the ability to ionize atoms or molecules.

Thus, the definition of ionizing radiation is precisely characterized by its capacity to create ions, which is why it is the correct answer.