Concept:Alpha decay reduces the mass number by 4 and the atomic number by 2.Explanation:Initial nucleus: 82210Pb; final nucleus: 80206Pb.Mass number change: 210−206=4.Atomic number change: 82−80=2.An alpha particle, 24He, has mass number 4 and atomic number 2, so only one alpha particle is emitted:82210Pb→80206Pb+24HeAnswer:an alpha particle.