Properties of transition metals
In general, the electronic configuration of outer orbitals of transition elements is (n-1)d1– 10 ns1–2. However, the electronic configurations of outer orbitals of Zn, Cd, Hg, and Cn are represented by the general formula (n-1)d1– 10 ns2. These metals are very hard and have low volatility due to high enthalpy of atomization. The more unpaired electrons, the higher the enthalpy of atomization. The stability of the half-filled d subshell in Mn2+ and the completely filled d10 configuration in Zn2+ are related to their E° values, whereas E° for Ni is related to the highest negative ΔhydH°.
Transition metals show highest oxidation state in its....
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → oxide
A metal can show a high oxidation state only with an element that is small and highly electronegative, so that it can remove many electrons from the metal. Oxygen and fluorine are the two such elements. Oxygen goes further than fluorine because it can form multiple (double) bonds with the metal, so one oxygen atom can take up two of the metal’s valencies.
Examples from the 3d series:
Manganese: \( \ce{Mn2O7} \) and \( \ce{MnO4^{-}} \) (+7), while its highest fluoride is only \( \ce{MnF4} \) (+4).
Chromium: \( \ce{CrO3} \) and \( \ce{Cr2O7^{2-}} \) (+6).
Vanadium: \( \ce{V2O5} \) (+5).
So transition metals show their highest oxidation state in their oxides (and oxoanions).
Why the other options are incorrect
Option (1) nitrate — Incorrect. Nitrate is a large ion with a single negative charge and cannot stabilise a very high oxidation state; metal nitrates show common, lower oxidation states such as +2 and +3.
Option (2) acetate — Incorrect. Acetate is also a bulky, singly charged ion, and the metal in acetates is usually in a low oxidation state.
Option (4) chloride — Incorrect. Chlorine is larger and less electronegative than oxygen and fluorine, so chlorides do not reach the highest oxidation states.
Note: It seems that there is a mistake in the original NTA paper, which prints the outer electronic configuration of Zn, Cd, Hg and Cn as (n−1)d1–10ns2 when it should read (n−1)d10ns2, because these metals have a completely filled d subshell. The next sentence, “These metals are very hard and have low volatility due to high enthalpy of atomization”, reads as if it describes Zn, Cd and Hg, but it is true of transition metals in general. Zn, Cd and Hg are soft and fairly volatile (mercury is a liquid) and have the lowest enthalpies of atomisation, because they have no unpaired d electrons for metallic bonding.
NCERT (2026-27 edition):
Trends in Stability of Higher Oxidation States – …
