The ion that is a single proton is called a hydrogen ion, represented by the symbol H⁺.

Here's why:

* Protons: Protons are positively charged particles found in the nucleus of an atom.

* Hydrogen Atom: A hydrogen atom has one proton and one electron.

* Hydrogen Ion: When a hydrogen atom loses its single electron, it becomes a hydrogen ion, which is essentially just a proton.

This is why hydrogen ions are sometimes referred to as simply "protons" in certain contexts.