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
484 exam-style questions on CIE IGCSE Physics 5.2 Radioactivity, covering 5.2.1 Background radiation and measuring count rate, 5.2.2a Alpha, beta and gamma emission, 5.2.2b Deflection and ionising effects of nuclear radiation, 5.2.3a Radioactive decay, 5.2.3b Effects of decay on the nucleus and decay equations, 5.2.4a Half-life, 5.2.4b Choosing isotopes for applications, and 5.2.5 Effects of ionising radiation and safety precautions. Each one has a worked solution and a mark scheme showing where the marks go.