28.1.1—Transition element

A transition element is a d-block element that forms one or more stable ions with an incomplete d subshell. The definition concerns ions, not merely the neutral atom’s position in the periodic table.

Check the electron configuration of the common ion. Zinc is d-block but Zn²⁺ is 3d¹⁰, so it is not a transition element under this definition.

Fe²⁺ is 3d⁶ and Fe³⁺ is 3d⁵, so iron qualifies; Sc³⁺ is d⁰ and does not meet the incomplete-d-ion criterion.

“d-block” and “transition element” are not synonyms in every syllabus definition.