Which of the following is a correct definition of the half-life of a radioactive isotope?
The time taken for the total mass of the sample containing the isotope to be reduced by half.
Half of the time taken for all of the radioactive nuclei in a sample to decay.
The time taken for the number of radioactive nuclei of that isotope in a sample to decrease to half of its initial value.
The time taken for the activity of the sample to decrease to zero.
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.