Let's match the standard electrode potentials (EM2+∕M⊖) for the given transition metals. We need to recall the typical values for these elements from the electrochemical series. The standard reduction potentials for the given metals are approximately: Manganese (Mn): EMn2+∕Mn⊖ is known to be significantly negative, typically −1.18V. This is due to its strong tendency to form Mn2+, especially considering the stable half-filled d -subshell (d5) in Mn2+ after losing two electrons from its [Ar]3d54s2 configuration. Chromium (Cr): ECr2+∕Cr⊖ is also quite negative, typically −0.91V. Iron (Fe): EFe2+∕Fe⊖ is moderately negative, typically −0.44V. Nickel (Ni): ENi2+∕Ni⊖ is the least negative among the given options, typically −0.25V.
