Here's why:

* Definition of Transition Elements: Transition elements are a group of elements located in the d-block of the periodic table. These elements have their outermost electrons in d orbitals, and they exhibit a range of oxidation states, forming colorful compounds, and often having catalytic properties.

* Copper's Properties: Copper is located in group 11 of the periodic table, which is within the d-block. It has an electronic configuration of [Ar] 3d¹⁰ 4s¹, which means it has a filled d-orbital and one electron in its outermost s-orbital. Copper can form ions with different oxidation states (Cu⁺ and Cu²⁺), demonstrating its characteristic transition metal properties.

Therefore, based on its position in the periodic table and its characteristic properties, copper is undeniably a transition element.