Correct relation among X_A, X_B and D, where X_A and X_B are the electronegativities of elements A and B.

The mathematical expression is written as:

$X_A-X_B=0.208∆$

$∆=E_{A-B}-\frac{1}{2}\left(E_{A-A}+E_{B-B}\right)$ 

where E_A-B is the bond dissociation energy of A-B.

Bond dissociation energy is expressed in kcal/mol.