One. A hydrogen ion (H+) has a +1 charge, and a chloride ion has a -1 charge, Cl-, so they combine in a 1-to-1 ratio to form a neutral compound, HCl or hydrochloric acid.
Hydrogen always has 1 proton. If it had two, it would then become Helium. The fact that it is a Hydrogen ion, just means that it is not electrically neutral. Since the proton is what defines the...