The Faraday laws of electrolysis state that the charge transported by a solvated ion between two electrodes is an integer multiple of the elementary charge e. Why this happens is far from obvious, because liquids are not assemblies of ions: they are assemblies of atoms, having ionic character only because the neighboring atoms have different ionicity. There is no way of extracting integer charges from a "snapshot" of the electronic charge distribution at a given time. Instead, integer charges manifest themselves only when the nuclei are adiabatically transported over macroscopic distances: a playground where topology--since Thouless' seminal work in the 1980s--has a major role.
Reference
[1] R. Resta, Faraday law, oxidation numbers, and ionic conductivity: The role of topology, arXiv:2104.06026 [cond-mat.mtrl-sci] (J. Chem Phys., in press).
Poděkování
Projekt OP VVV Mobilita výzkumných pracovníků FZU, reg. č. CZ.02.2.69/0.0/0.0/18_053/0016627.