* Polyvalent refers to elements that can form multiple ionic charges. This is typically associated with non-metals like phosphorus or sulfur, which can form anions with different charges depending on the compound.

* Transition metals are known for having multiple oxidation states (not ionic charges). This means they can form cations with different charges in their compounds. Nickel, for example, commonly has oxidation states of +2 and +3, forming compounds like NiO (nickel(II) oxide) and Ni2O3 (nickel(III) oxide).

Therefore, nickel is not a polyvalent metal. Instead, it is a transition metal with multiple oxidation states.