Here's why:

* Salts are formed from the reaction of an acid and a base. Ferrous sulfate is formed by the reaction of sulfuric acid (H₂SO₄) and ferrous hydroxide (Fe(OH)₂).

* Salts can be acidic, basic, or neutral depending on the strength of the acid and base that formed them. In the case of ferrous sulfate, both sulfuric acid and ferrous hydroxide are strong, so the resulting salt is neutral.

However, a solution of ferrous sulfate in water will be slightly acidic. This is because the ferrous ion (Fe²⁺) can hydrolyze in water, meaning it reacts with water molecules to form hydronium ions (H₃O⁺), which make the solution acidic.

Therefore, while ferrous sulfate itself is not an acid or base, its solutions can be slightly acidic.