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Q.
Which of the following has highest second ionization energy?
ManipalManipal 2008Classification of Elements and Periodicity in Properties
Solution:
Electronic configuration of chromium is $1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{6} 3 d^{5} 4 s^{1}$
We can remove the $1^{\text {st }} e ^{-}$from valency shell $4 S ^{1}$ is very easily. So, the $1^{\text {st }}$ ionisation potential is very low.
$\Rightarrow $ But for removing $2^{\text {nd }}$ electron it requires more energy because $3 d ^{5}$ is half filled. So, it have high second ionisation potential.