Hi Soumya,

Fajans rule is used to predict whether a chemical bond will be covalent or ionic

Fajan's discussed more about covalent and ionic character by some rules 

• The smaller the size of the cation and the larger the size of the anion, the greater the covalent character of an ionic bond.

• The greater the charge on the cation, the greater the covalent character of the ionic bond.

• For cations of the same size and charge, the one, with electronic configuration (n-1)dnnso, typical of transition metals, is more polarising than the one with a noble gas configuration, ns2 np6, typical of alkali and alkaline earth metal cations.

For better understanding you can visit NEET Series - https://youtu.be/_aTG3vOr_8E?t=1338

Or Our One shot series  - https://youtu.be/-jCWL5v-rHs?t=5049

Hope you got your answer

Thanks for asking