#2943: Unsolved Chemistry Problems

XKCD comic, described below.
Transcript

[Hairbun stands behind a lectern on a podium speaking into a microphone on the lectern. A Cueball like guy stands to the left and another Cueball like guy and Megan stand to the right. There is a large sign hanging in the background along with some ornaments.]

Sign: Grand Opening

Hairbun: Our lab will be working on chemistry's top unsolved problems: arbitrary enzyme design, protein folding, depolymerization, and, of course, the biggest one of all:

Hairbun: Figuring out what the "p" in "pH" stands for.

(Sourced from explainxkcd.com)

I'm an H⁺ denier, in that I refuse to consider loose protons to be real hydrogen, so I personally believe it stands for 'pretend'.

ExplainOriginal