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describe the direction of electron flow between electrodes when a switch is closed.

Electrons flows from negative electrode which is called cathode to positive anod. When switch is closed electrons flow is like that. But we dont use it in International system. In International system we choose the way of flowing positive ions. Positive ions dont generally move inside metals, but if it did than it would be from positive anod to negative cathode. So In International system we use this system.

Outermost (valence) electrons