Video narration
At an electrode, if several ions could react, which one do you think gets chosen? Imagine waiting in a queue where several people need service: the ions compete for a chance to react, though they do not literally take turns. That preference is called preferential discharge: one ion reacts instead of other ions that could react there. At the cathode, positive ions gain electrons; at the anode, negative ions lose electrons. But the first ion to arrive does not win. Conditions change the choice. The electrochemical series helps indicate which reactions are favored, while concentration and electrode material also influence what happens. These factors work together; none is a universal rule that picks the winner in every solution. So which ion reacts? The one favored by the conditions: its place in the electrochemical series, its concentration, and the electrode material.