Debye–Hückel
Debye–Hückel theory concerns non-ideal electrolyte solutions. Containing ions, they are pretty hard to describe mathematically.
Personally, I wouldn’t try to attempt it, and apparently no one else wants to either, since you can legally just throw an activity coefficient into the solution’s equations and call it a day.
Alternate: A bit more neon…
A more spectral version:
