Question

The elements most likely to form more than one type of ion are the
-transition metals.
-alkali metals.
-halogens.
-alkaline earth metals.

Answer 1

-transition metals.

Answer 2

Yes, I'd say transition metals, too. Halogens have a charge of -1, alkali metals +1. earth alkali metals +2. Transition metals can have more types due to d-Orbitals, like in FeO (Fe = +2) or in Fe_3O_2 (Fe = +3).