Q48 / 180 · COMEDK 2026 (9 May Shift 2) · Chemistry
The element with the highest third ionisation enthalpy is:
- Correct answerAManganese (Z=25)
- BVanadium (Z=23)
- CIron (Z=26)
- DChromium (Z=24)
Solution
The electronic configurations of the given elements and their divalent ions are:
Mn (Z=25): $[Ar] 3d^5 4s^2 \rightarrow Mn^{2+}: [Ar] 3d^5$
V (Z=23): $[Ar] 3d^3 4s^2 \rightarrow V^{2+}: [Ar] 3d^3$
Fe (Z=26): $[Ar] 3d^6 4s^2 \rightarrow Fe^{2+}: [Ar] 3d^6$
Cr (Z=24): $[Ar] 3d^5 4s^1 \rightarrow Cr^{2+}: [Ar] 3d^4$
The third ionization enthalpy is the energy required to remove an electron from the $+2$ ion.
$Mn^{2+}$ has a stable half-filled $3d^5$ configuration. Removing an electron from this highly stable configuration requires a very high amount of energy.
Therefore, Manganese has the highest third ionization enthalpy among the given elements.
Answer: Manganese (Z=25)
Mn (Z=25): $[Ar] 3d^5 4s^2 \rightarrow Mn^{2+}: [Ar] 3d^5$
V (Z=23): $[Ar] 3d^3 4s^2 \rightarrow V^{2+}: [Ar] 3d^3$
Fe (Z=26): $[Ar] 3d^6 4s^2 \rightarrow Fe^{2+}: [Ar] 3d^6$
Cr (Z=24): $[Ar] 3d^5 4s^1 \rightarrow Cr^{2+}: [Ar] 3d^4$
The third ionization enthalpy is the energy required to remove an electron from the $+2$ ion.
$Mn^{2+}$ has a stable half-filled $3d^5$ configuration. Removing an electron from this highly stable configuration requires a very high amount of energy.
Therefore, Manganese has the highest third ionization enthalpy among the given elements.
Answer: Manganese (Z=25)
Hence, the correct answer is option: 'A'.