The correct statement about radioactive decay is:
More of the radioactivity is lost during the first half-life than in later half-lives.
In radioactive decay, every half-life is a period during which half of the remaining radioactive atoms decay. Therefore, during the first half-life, a significant portion of the substance decays relative to the total amount present, while in subsequent half-lives, the amount of material left decreases, so the absolute amount that decays becomes less, even though it still represents half of what remains at that time.
The other statements are incorrect:
- More of the radioactivity is not lost during the fourth half-life than in the first half-life; each half-life consistently results in half of the remaining substance decaying.
- Isotopes do not become more stable during the first half-life; they are decaying over time, indicating they are unstable.
- Isotopes also do not become "least stable" in the later half-lives; rather, they decay over time towards stability.