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Q.
Which of the following has highest second ionisation energy
ManipalManipal 2019
Solution:
The electronic configuration of ${ }_{24} C_{r}$ is $[ Ar ]_{18} 3 d_{1}^{5} 4 s^{1}$. Chromium after loss of one electron gain stable configuration due to presence of half filled d-orbitals, therefore its second ionisation enthalphy is highest.