Which of the following is a correct definition of the half-life of a radioactive isotope?
The time taken for the total physical mass of the sample to decrease to half of its original value.
The time taken for the activity of a sample of the isotope to decrease to half of its initial value.
Half of the total lifetime of all the radioactive atoms in the sample.
The time taken for the number of protons in each unstable nucleus to reduce by half.
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.