An element is classified as a transition metal if it possesses an incompletely filled d-subshell, whether in its fundamental state or in any of its ionized forms. - Zinc (Zn) exhibits the electronic configuration: [Ar] 3d\(^{10}\) 4s\(^{2}\). Its d-orbital is entirely filled in both its elemental form and its usual oxidation state (+2). Consequently, it is not categorized as a transition metal. - Iron (Fe), Chromium (Cr), and Copper (Cu) all feature partially filled d-orbitals in their common oxidation states, thereby meeting the criteria for transition metals.