How is the concept of half-life best described?

The concept of half-life is best described as the time needed for half of the radioactive atoms in a sample to decay. This is a fundamental principle in radioactive decay, which states that during each half-life, a specific percentage of the original radioactive material will transform into a different element or isotope. Therefore, if you start with a certain number of radioactive atoms, after one half-life, only half of those atoms will remain as radioactive material, while the other half will have decayed.

This definition reflects the probabilistic nature of radioactive decay, where each atom has a chance of decaying independent of one another. Consequently, a sample doesn't decay all at once; rather, it will see a consistent decrease in the amount of the radioactive substance over repeated half-lives. The term "half-life" specifically signifies this relationship, making the correct answer a precise representation of the concept in the context of radiation safety and understanding the behavior of radioactive substances.