question_answer

What percentage of a given mass of a radioactive substance will be left undecayed after five half-life periods?            

Answer:

                Here, number of half-life periods \[(n)=5\] \[\therefore \]                \[\frac{N}{{{N}_{0}}}=\frac{1}{{{2}^{n}}}=\frac{1}{{{2}^{5}}}=\frac{1}{32}=\mathbf{3}\mathbf{.125%}\]