39/19 K, avem:
Z = 19 => 19 p+ , 19 e-
stim ca A = Z + n0 => n0 = A - Z
= 39 - 19 = 9 n0
63/39 Cu, avem:
Z = 39 => 39 p+ , 39 e-
stim ca A = Z + n0 => n0 = A - Z
= 63 - 39 = 24 n0
56/26 Fe, avem:
Z = 26 => 26 p+ , 26 e-
stim ca A = Z + n0 => n0 = A - Z
= 56 - 26 = 30 n0