What is the source of the ions involved in a redox reaction that occurs in an electrochemical cell?

D. Electrodes

Explanation:

A redox reaction is defined as the reaction in which both oxidation and reduction reactions take place and electrons are transferred from oxidized substance to the substance that is being reduced.

An electrochemical cell is consist of electrodes (anode and cathode), electrolyte solution, salt bridge, and conducing wire. An electrochemical cell undergoes redox reaction that produces an electric current due to the movement of ions through electrodes. Electrodes are the source of ions, as anode electrode undergoes oxidation reaction and releases electrons or ions and cathode, gains electrons through reduction reaction.

Hence, the correct answer is "D. Electrodes".