Configurations, oxidation states and who counts as a transition element

Chemists use a test, not only the position in the table: an element is a transition element if its atom, or at least one of its common ions, has a partly filled d sublevel (1 to 9 electrons in d). Apply it. Iron: the atom is 3d⁶, so yes. Scandium: the atom is 3d¹, so yes, although Sc³⁺ has no d electrons; one case is enough. Copper: the atom is 3d¹⁰, which is full, but Cu²⁺ is 3d⁹, partly filled, so copper counts. Gold: Au³⁺ is 5d⁸, so gold counts. Zinc: the atom is 3d¹⁰ and its only common ion Zn²⁺ is also 3d¹⁰, so zinc is in the d block but is not a transition element; the same holds for cadmium and mercury. Silver is a borderline case: Ag⁺ is 4d¹⁰, and only the rare Ag²⁺ (4d⁹) makes it a transition element, which is why courses treat it with care (extra). So the d block and the transition elements are nearly, but not exactly, the same set.