Question

the time that it takes for half of a radioactive isotope to change into another stable element is its multiple choice half-life. chemical life cycle. activation time. life span.

Explanation:

The question is about a concept in radioactive decay. The definition given matches the term "half - life", which is the time required for half of a radioactive isotope to decay (change into another stable element). "Chemical life cycle" is not related to radioactive decay, "activation time" has no relation to this context, and "life span" is about the duration of existence of a living thing or a non - living entity in a non - radioactive decay sense.

Answer:

A. half - life