Question

Which of the following has highest second ionization energy?

• A. Calcium
• B. Chromium
• C. Iron
• D. Cobalt

Answer 1

Answer: (B)

Electronic configuration of chromium is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{5}4s^1$
We can remove the $1^{\text{st }}{e}^{-}$from valency shell $4S^1$ 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 $3d^5$ is half filled. So, it have high second ionisation potential.