Here's why:

* Ferrous refers to the iron(II) ion, which has a charge of +2 (Fe²⁺).

* Sulfate is the polyatomic ion SO₄²⁻, with a charge of -2.

To form a neutral compound, the charges must balance. Since the sulfate ion has a -2 charge, the ferrous ion needs a +2 charge to cancel it out.

Therefore, the chemical formula for ferrous sulfate is FeSO₄.