WAEC Chemistry 2011 Paper

Concept:A positive electrode potential means $M^{2+}/M$ has a greater tendency to gain electrons than $H^+/H_2$.Explanation:For the cell $M(s)|M^{2+}(aq)||H^+(aq)|H_2(g)$, a positive potential indicates that reduction of $M^{2+}$ is preferred over reduction of $H^+$.Thus, $M(s)$ acts as the cathode (positive electrode) and accepts electrons.The hydrogen electrode, $H_2(g)$, acts as the anode (negative electrode) and loses electrons.In the external circuit, electrons always flow from the negative electrode to the positive electrode.Therefore, electrons flow from the hydrogen electrode to the metal electrode.Answer:Option B: electrons flow from hydrogen electrode, $H_2(g)$, to metal electrode, $M(s)$.