[aristomc]

"Chemistry answers that H2 and O2 can be joined to form water under certain conditions, but doesn't answer the whys".

Chemistry does answer the whys beyond product yields, why certain elements react is vastly covered throughout organic, inorganic & physical chemistry . It is the basis of these sub-fields, and how this is determined is looking at orbitals, energy states etc...

[raverbashing]

Yes, there's an overlap of knowledge

So, Pauli's exclusion principle is Physics or Chemistry? I'd say it's "both".

[xerophtye]

Physical Chemistry. (its a real thing)