What is meant by radioactivity?

Radioactivity refers specifically to the process by which unstable isotopes undergo decay, leading to the emission of radiation. This phenomenon occurs when the nucleus of an atom is unstable and seeks stability through the release of energy in the form of particles or electromagnetic waves. This decay can take various forms, including alpha decay, beta decay, and gamma decay.

Understanding radioactivity is crucial because it has significant implications in various fields, such as medicine, where radioactive materials are used in diagnostic imaging and treatment, as well as in environmental science, where it plays a role in understanding nuclear waste management and radiation protection.

The other options do not accurately reflect the definition of radioactivity. The formation of stable isotopes over time does not encapsulate the essence of radioactivity, as it focuses on stability rather than the decay process. Bonding atoms together relates to chemical interactions and is unrelated to the nuclear processes involved in radioactivity. Lastly, nuclear fusion is a different process where two light atomic nuclei combine to form a heavier nucleus, releasing energy, but it is not a definition of radioactivity.