Hydrogen bonding plays a central role in the following phenomena:

A] Ice has cage-like structure in which each water molecule is surrounded by four other water molecules tetrahedral through hydrogen boding, due to this density of ice is less than water and it floats in water.
B]


The cation (I) more stabilized through hydrogen boding than cation II . So, $\mathrm{R}-\mathrm{N}{\mathrm{H}}_2$ is better base than ${\left(\mathrm{R}\right)}_3\mathrm{N}$ in aqueous solution.
C] HCOOH is stronger acid than $\mathrm{C}{\mathrm{H}}_3\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{H}$ due to inductive effect and not due to hydrogen bonding.
D] Acetic acid dimerizes in benzene through intermolecular hydrogen bonding.