Here's why:

* Chemical Composition: Ferric ammonium sulfate (FeNH₄(SO₄)₂) is a compound made up of multiple elements: iron (Fe), ammonium (NH₄), sulfur (S), and oxygen (O).

* Metals vs. Compounds: Metals are pure elements found on the periodic table. Compounds are formed when two or more elements chemically bond together.

* Properties: Ferric ammonium sulfate is a salt, a type of ionic compound that typically dissolves in water. Metals are usually solid at room temperature and have characteristic metallic properties like conductivity and malleability.

In summary: Ferric ammonium sulfate is a compound, not a metal. It is made up of various elements bonded together and has properties distinct from metals.