Explanation

The question asks for equivalent masses based on valency. 1 mg of H+ (valency 1) is equivalent to 20 mg of Ca2+ (valency 2, atomic mass 40), 12 mg of Mg2+ (valency 2, atomic mass 24), and 9 mg of Al3+ (valency 3, atomic mass 27). All options represent the same number of equivalents.