Which of the following is a correct definition of the half-life of a radioactive isotope?
Half of the time required for all the radioactive nuclei in a sample to decay
The time required for the activity of a radioactive sample to decrease to half of its initial value
The time required for the mass of an individual unstable nucleus to halve
The average time a single radioactive nucleus exists before it decays
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.