Question

The half life of a radioactive element is 10 years. What percentage of it will decay in 100 years?

• A. 99.9 %
• B. 10 %
• C. 50 %
• D. 66.5 %

Answer 1

Answer: (A)

99.9 %

The half life period is 10 years. 100 years corresponds to $\frac{100}{10}=10$ half life periods.

The percentage of radioactive substance that will decay in 10 half life periods is $100-\frac{100}{2^{10}}=99.9$ %