How is a hydrogen bond formed? Give the reason for the formation of a hydrogen bond with an example.

(N/A) hydrogen bond is formed when a hydrogen atom is covalently bonded to a highly electronegative atom $(X)$ such as $N, O,$ or $F$.
Reason for formation: When hydrogen is bonded to a strongly electronegative element '$X$',the shared electron pair is pulled towards the electronegative atom. This causes the hydrogen atom to acquire a partial positive charge $(+\delta)$ and the electronegative atom to acquire a partial negative charge $(-\delta)$. This creates a dipole,and the electrostatic force of attraction between the partial positive hydrogen of one molecule and the partial negative electronegative atom of another molecule is called a hydrogen bond.
Representation: $A$ hydrogen bond is represented by a dotted line $(\ldots)$,while a solid line $(-)$ represents a covalent bond.
Example: In hydrogen fluoride $(HF)$,the interaction is represented as: $H^{\delta+} - F^{\delta-} \ldots \ldots H^{\delta+} - F^{\delta-}$