Question

The transition metal having highest $3^\text{rd}$ ionisation enthalpy is:

• A. Cr
• B. Mn
• C. V
• D. Fe

Answer 1

Answer: (B)

Mn

Answer 2

The 3rd ionisation enthalpy refers to the energy required to remove the third electron after the removal of the first and second electrons from a neutral atom.
Reasoning for Mn Having the Highest 3rd Ionisation Enthalpy
Manganese (Mn) has the electronic configuration [Ar] $3d^5 4s^2$.
The removal of the first and second electrons leads to a half-filled $3d^5$ configuration, which is highly stable due to symmetrical distribution and exchange energy.
Removing the third electron from this stable half-filled $3d^5$ configuration requires a significantly higher amount of energy compared to other transition elements such as Cr, V, and Fe.
Conclusion: The transition metal having the highest 3rd ionisation enthalpy is Mn.