Number of electrons in the outermost shell = 5
Number of electrons required to make noble gas configuration = 8 – 5 = 3
The charge on the ion so formed = Z + 3e–
= Z3-
The valency of Z = 3
Chemical formula of the compound:

Number of electrons in the outermost shell = 5
Number of electrons required to make noble gas configuration = 8 – 5 = 3
The charge on the ion so formed = Z + 3e–
= Z3-
The valency of Z = 3
Chemical formula of the compound:

| Elements | Protons | Electrons | Neutrons | Atomic Number | Mass Number |
| A | – | – | 10 | 8 | – |
| B | 15 | – | – | – | 31 |
| C | 1 | – | – | – | 3 |
| D | – | 11 | 12 | – | – |
| X | Y | |
| Protons | 8 | 8 |
| Neutrons | 8 | 10 |