3. Укажите состав атомных ядер изотопов: а) 12 24Mg; 12 25Mg; 12 27Mg; б) 16O; 17O;18O.

а)
Z = 12, A = 24, N = 12
Z = 12, A = 25, N = 13
Z = 12, A = 27, N = 15

б)
Z = 8, A = 16, N = 8
Z = 8, A = 17, N = 9
Z = 8, A = 18, N = 10