Option D — Zinc
Zinc is more reactive than iron but less reactive than aluminium in the activity series, so it displaces Fe from FeSO₄ but cannot displace Al from Al₂SO₄.
The activity series order is: Al > Zn > Fe > Cu. A metal displaces only those metals that are below it in the series. Zinc is below aluminium (cannot displace it) but above iron (can displace it). Magnesium is above both, so it would displace both. Copper and Lead are below iron, so they cannot displace iron either. Zinc is the only option that fits both conditions in the question.