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Conditions for ranking of negative ion discharge order

My teacher told us about the negative ion discharge order

$$\ce{SO4^2-} < \ce{NO3-} < \ce{OH-} < \ce{Cl-} < \ce{Br-} < \ce{I-}$$

in the sense which ion would discharge to electrodes first in a mixture. For example, $\ce{NaCl(aq)}$ solution where $\ce{Cl-}$ ion would get discharged before $\ce{OH-}$ ion. Similarly, $\ce{H+}$ ion would be reduced to $\ce{H2}$ (gets to the cathode before $\ce{Na+}$ ion).

What factors does this order depend upon?

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