pt. elementul C
1s2 2s2 2p4 => Z.C = 8
A = 2B
A-C = 4 => 2B-8 = 4
=> B = 12/2 = 6 => Z.B= 6
A = 2B = 12 => Z.A = 12
A = Mg, B = C, C = O
b)
Mg are sarcina nucleara = +12
C are sarcina nucleara = +6
O are sarcina nucleara = +8
c)
Mg, 1s2 2s2 2p2 3s2
C, 1s2 2s2 2p2
O, 1s2 2s2 2p4
d)
Mg, 2
C, 1
O, 1