Answer:
The correct answer is because there are polyvalent metals.
Step-by-step explanation:
Most transition metals can form cations with various loads. That is why block d of the periodic table is marked as "variable load". For example, iron is polyvalent, which means "many values", i.e. it can form cations with different loads. For polyvalent metals, we must specify the magnitude of the ion charge. In the case of anions most of the time it is not necessary to specify the magnitude of the charge of the anion.
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