Because redox reactions are defined in terms of oxidation numbers, performing a demonstration that illustrated several oxidation states for an element is useful. There are several demonstrations that illustrate this using transition elements, ones that tend to be colorful due to a variety of color-generating mechanisms, especially those involving transitions of d electrons.

Showing several oxidation states of vanadium is very colorful. Oxidation States of Vanadium: Reduction of V⁵⁺ to V²⁺

Oxidation States of Chromium