Question

which describes radioactive decay of a substance?
more of the radioactivity is lost during the first half - life than in later half - lives.
more of the radioactivity is lost during the fourth half - life than in the first half - life.
isotopes are the most stable during the first half - life.
isotopes are the least stable during the later half - lives.

Explanation:

Radioactive half-life means in each half-life period, half of the remaining radioactive substance decays. In the first half-life, we start with the full amount, so half of the total original radioactivity is lost. In subsequent half-lives, we only lose half of the remaining (smaller) amount, so less radioactivity is lost per later half-life. Isotope stability does not change across half-lives, and later half-lives do not involve more decay than the first.

Answer:

A. More of the radioactivity is lost during the first half-life than in later half-lives.