Final answer:
The negatively charged electrode during an electrotherapy treatment is known as the (2) cathode.
Step-by-step explanation:
The electrode that is negatively charged during an electrotherapy treatment is known as the cathode. In the context of electrochemical cells, the terms anode and cathode have specific meanings tied to the process of oxidation and reduction. In an electrolytic cell, which is typically used in electrotherapy treatments, the anode is positive because it is connected to the positive terminal of the battery, which makes the cathode negative.
Therefore, when reduction occurs, it takes place at the cathode, which gains mass due to material deposit, and the concentration of ions in the solution decreases as the reaction progresses.
In an electrolytic cell, electrons flow through the cell from the anode to the cathode since the anode is the site of oxidation, where electrons are 'produced' and leave the cell, and the cathode is the site of reduction, where electrons are utilized. This flow of electrons creates a negative charge at the electrode where reduction occurs, solidifying the cathode's role as the negative electrode in an electrolytic setting.