A scientific laboratory accidentally releases a small quantity of the radioactive isotope cobalt-60, 2760Co^{60}_{27}\text{Co}2760Co. After a period of 21.2 years, the activity of the cobalt-60 in the facility has decreased to 6.25% of its original value.
What is the half-life of cobalt-60?
4.2 years
5.3 years
7.1 years
10.6 years
144 exam-style questions on CIE IGCSE Physics 5.2.4a Half-life. Each one has a worked solution and a mark scheme showing where the marks go.