Concept:Fajans' Rules dictate that high polarizing power (small cation with a high charge) pulls the electron cloud of an anion toward itself, introducing significant covalent character into an otherwise ionic bond.
Solution:- All the options are nitrides of Group 2 metals.
- As we move up Group 2, the size of the cation decreases drastically.
- Beryllium (\( \text{Be}^{2+} \)) is the smallest cation in the group. Because of its tiny radius and +2 charge, it possesses an intensely high charge density (polarizing power).
- When bonded to Nitrogen, \( \text{Be}^{2+} \) severely distorts Nitrogen's electron cloud, sharing the electrons rather than fully transferring them.
- Therefore, \( \text{Be}_3\text{N}_2 \) exhibits predominantly covalent characteristics, unlike the other highly ionic nitrides in the group.
Why other options are incorrect:- The cations Mg, Ca, and Ba are much larger. Their lower polarizing power results in bonds that are overwhelmingly ionic.
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