Number of electrons in Na atom = Atomic number = 11
Number of electrons in Na+ ion = 1 1 – 1 = 10
Electronic configuration of Na+ ion: 2, 8
Number of electrons in Na atom = Atomic number = 11
Number of electrons in Na+ ion = 1 1 – 1 = 10
Electronic configuration of Na+ ion: 2, 8
| 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 |