(a) Mn2+ has a d5 configuration, and the extra stability of half-filled d-orbitals is comprised when another electron is taken out to give Mn3+, On the other contrary, Fe3+ attains a half-filled orbitals configuration when Fe3+ gets oxidized to Fe3+ . Hence, the Eo value for Mn3+/Mn2+ couple has more positive Eo value.
(b) Fe has 3d64s2 outer electronic configuration whereas Cu has 3d104s1 configuration. Now, more the number of unpaired electrons in d-orbital, more favourable are interatomic attractions and thus higher atomization enthalpies. Hence, Fe has4- unpaired d-electrons has more enthalpy of atomization than copper having no unpaired d electron.
(c) Sc3+ has 3d10 configuration whereas Ti3+ has a 3d1 configuration. As there are no electrons in d-orbitals for Sc3+ ion, there is no transition of electrons y absorption of energy and hence no emission in visible range imparting colour to the Sc3+
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