Hydrogen bond — হাইড্রোজেন বন্ধন
A weak attraction in which hydrogen bonded to O, N or F is pulled toward a lone pair on a neighbouring electronegative atom.
Definition
A hydrogen bond is not a full chemical bond but a strong dipole attraction. When hydrogen is covalently bonded to a small, electron-hungry atom such as oxygen, nitrogen or fluorine, it carries a large partial positive charge, so it is drawn toward a lone pair on an electronegative atom of a neighbouring molecule. Each hydrogen bond is weak on its own, yet together they give water its high boiling point, make ice float on pond water, hold DNA's double helix together, and keep proteins folded.
For example
Water boils at 100 °C only because each molecule hydrogen-bonds to roughly four neighbours; without them, a glass of water would evaporate away at kitchen temperature.