Question

What percentage of a radioactive isotope remains after 20.0 days if its half life is 10.0 days?

Answer 1

25 %

Step-by-step explanation:

20 days would mean that there are 2 half lives within that period since the half life is 10 days. After the first half life 50% of the substance remains. After another half life 0.5(50) = 25% remains