Question

In aqueous solution, the proton exists as a ___ (acid/base).

Answer 1

The hydrogen ion in aqueous solution is no more than a proton, a bare nucleus.

Although it carries only a single unit of positive charge, this charge is concentrated into a volume of space that is only about a hundred-millionth as large as the volume occupied by the smallest atom.

This proton would act as an acid in an aqueous solution, not as a base. So the correct answer is Acid.