Science question about chemicals. 10 pts. best answer.?

Hard to say. Those are not standard chemical names.

H4 doesn't mean anything, chemically speaking.

H2 is the symbol for hydrogen gas, but clearly hydrogen was never kept in a vat, so the label must mean something else.

What you're looking at must be labels for the vats. It implies that there are/were vats H1 and H3 somewhere.

In any case "H2" and "H4" tell you nothing about the former contents of the vats.