Question

What is the strongest known acid?

Answer 1

Triflic acid is fairly dangerous, with `"pK"_a ~~ -14`. Anything with fluorides coordinated around it will increase a compounds acidity due to the dipole.

Fluoroantimonic acid is probably one of the (if not the) most acidic species, with `"pK"_a ~~ -31.3`.

Those hydrogens on that fluorine are extra nasty, they'll protonate even hydrocarbons I'd imagine. For comparison, sulfuric acid is a typical strong acid, with `"pK"_a ~~ -3`.