$Cr = 1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}3{d^5}4{s^1}$
$Mn = 1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}3{d^5}4{s^2}$
$Fe = 1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}3{d^6}4{s^2}$
In second ionization enthalpy $C{r^ + }$ has exact half filled $d-$ sub shell.
$[M$ એ લેન્થેનોઈડ ધાતુ છે.]