13.
Ra decays with a half-life of 1600 s.Rn decays with a half-life of 52 s.Po decays with a half-life of 9.1 s.Pb decays with a half-life of 10.6 h.The changing count rate for one of these radioactive nuclides is shown in the graph.From the half-life shown by the graph, which was the decaying radioactive nuclide?