Radioactive decay is a random process. What does this mean?
It is impossible to say which nucleus in the sample will decay next
Every nucleus in the sample decays at exactly the same moment
Each nucleus in the sample decays once during every half-life
The number of decays each second is the same for every source
40 exam-style questions on AQA GCSE Physics 4.2 Atoms and nuclear radiation, covering 4.2.1 Radioactive decay and nuclear radiation, 4.2.2 Nuclear equations, 4.2.3 Half-lives and the random nature of radioactive decay, and 4.2.4 Radioactive contamination. Each one has a worked solution and a mark scheme showing where the marks go.