Match List-I with List-II for the standard electrode potentials, E°(M3+/M2+), of the first row transition metals.
| List-I (Observation) | List-II (Reason) |
|---|---|
| (A) Low E°(M3+/M2+) value of scandium | (I) Stability of the half-filled t2g level of the M2+ ion |
| (B) Highest E°(M3+/M2+) value, for zinc | (II) Noble gas configuration of the M3+ ion |
| (C) Comparatively high E°(M3+/M2+) value of manganese | (III) Removal of an electron from the stable d10 configuration of the M2+ ion |
| (D) Comparatively low E°(M3+/M2+) value of vanadium | (IV) Particular stability of the d5 configuration of the M2+ ion |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A-II, B-III, C-IV, D-I
E°(M3+/M2+) measures how readily M3+ takes an electron to become M2+. A low value means M3+ is the stable ion; a high value means M2+ is stable and is hard to oxidise to M3+.
(A) Low E°(M3+/M2+) value of scandium — This matches (II) Noble gas configuration of the M3+ ion. Sc (3d14s2) loses all three outer electrons to give Sc3+ with the argon configuration, so Sc3+ is very stable.
(B) Highest E°(M3+/M2+) value, for zinc — This matches (III) Removal of an electron from the stable d10 configuration of the M2+ ion. Zn2+ is 3d10; forming Zn3+ would break this completely filled set, so Zn3+ readily goes back to Zn2+.
(C) Comparatively high E°(M3+/M2+) value of manganese — This matches (IV) Particular stability of the d5 configuration of the M2+ ion. Mn2+ is 3d5 (half-filled), so it resists oxidation to Mn3+.
(D) Comparatively low E°(M3+/M2+) value of vanadium — This matches (I) Stability of the half-filled t2g level of the M2+ ion. V2+ is 3d3; its three d electrons half-fill the t2g level.
NCERT (2026-27 edition):
4.3.6 Trends in the M3+/M2+ Standard Electrode Potentials – “…The low value for Sc reflects the stability of Sc3+ which has a noble gas configuration. The highest value for Zn is due to the removal of an electron from the stable d10 configuration of Zn2+. The comparatively high value for Mn shows that Mn2+(d5) is particularly stable, whereas comparatively low value for Fe shows the extra stability of Fe3+ (d5). The comparatively low value for V is related to the stability of V2+ (half-filled t2g level, Unit 5).”