Describe the law of Fajan's rule.

(N/A) Fajan's rule is used to predict the covalent character in an ionic bond. The rules are as follows:
$1$. Smaller size of the cation: $A$ smaller cation has a higher charge density,which increases its polarizing power.
$2$. Larger size of the anion: $A$ larger anion is more easily polarized by the cation due to its loosely held valence electrons.
$3$. Higher charge on the cation or anion: An increase in the charge on either the cation or the anion increases the extent of polarization.
$4$. Electronic configuration of the cation: Cations with a pseudo-noble gas configuration (e.g.,$Cu^+$,$Ag^+$,$Zn^{2+}$) have a greater polarizing power than those with a noble gas configuration (e.g.,$Na^+$,$K^+$) due to the poor shielding effect of $d$-electrons.