What is the definition of half-life?

The definition of half-life specifically refers to the time required for half of the nuclei of a particular radioactive isotope to decay. This is a crucial concept in nuclear chemistry because it helps in understanding how quickly a radioactive substance will decrease in quantity over a specified period.

The half-life is unique to each isotope, allowing scientists and chemists to predict the behavior of radioactive elements over time. The decay process is random for individual nuclei, but the average time calculated for half of a large number of nuclei to decay gives us valuable insight into the stability and longevity of the substance.

Other options, while they may reference decay or stability, do not accurately capture the essential concept of half-life. For instance, focusing solely on the entire substance decaying does not account for the gradual nature of radioactive decay described by half-life. Similarly, reaching a stable state or discussing the instability of atoms does not relate to the statistical nature of half-life and its specific measurement related to half of the nuclei.