- Cu2+
- Fe3+
- Na+
- Cr3+
Solution: Na+
Cu2+ = 1s22s22p63s23p63d9
Fe3+ = 1s22s22p63s23p63d5
Cr3+ = 1s22s22p63s23p63d3
Na+ = 1s22s22p6
All the given ions except Na+ have unpaired electrons in their outermost shells ( odd number of electrons). Therefore, sodium ion is the diamagnetic ion.