3. Classification of elements and periodicity in properties — Chemistry STD 11 Science — Question

If we note the ions formed because of the removal of $1$ electron from each of the above will be like this,

$Cr +, Mn +, Fe +$ now note its electronic configuration

For $Cr$ after one electron removal it is $4 s^0 \,3 d^5$ while before removal of electron it was $4 s^{13} d^5$ so by removal of one electron we get a stable specie, as $d 5$ is a stable system , and further removal will require high energy. The $2 nd\, IE$ for $Cr$ is $1590.69\, kJ / mol$

For Iron its normal config is $4s^2\,3 d^6$, while after $1^{st}$ $I.E$ it will lose its valence electron and will become $4 s^{13}\, d^6$ thus the resulting specie isn't that much stable as it is niether half filled nor full filled, so second ionization energy would be a bit lower, so its second IE is $1562.98\, kJ / mol$

While manganese has electronic config of $4 s^{23}\, d^5$ after removal of one electron we get a stable specie with config $4 s^{13}\, d^5$ which is half filled a comparatively stable one

. So its second IE would be $1509.03 \,KJ / mol$