Question

What is the half-life of a radioisotope if it decays to 25% of its original activity in 7 yr?

Answer 1

3.5 yrs

Step-by-step explanation:

If a sample has decayed to 25%, this means 2 half-lives have passed. We are given this is equal to 7 yrs, and it follows that one half life is 3.5 yrs.