How is radioactive decay best defined?

Radioactive decay is best defined as the process through which unstable atomic nuclei lose energy by emitting radiation. This transformation can involve various forms of radiation, including alpha particles, beta particles, or gamma rays, which can lead to the change of one element into another or a different state of the same element.

While radiation is a broad category that encompasses all types of emissions during decay, the essence of radioactive decay is tied to the change in the nucleus of the atom itself, resulting in the emission of energy as the atom seeks a more stable state. This definition captures the transformative aspect inherent in the decay process, making it fundamentally linked to the idea of radiation as a key outcome of the decay process.

It's important to note that while other choices provide specific aspects related to decay (such as emission of particles and release of gamma rays), they do not encompass the entire process as effectively as the concept of radiation, which highlights both the nature of energy loss and the resultant changes to the atomic structure.