Four successive members of the first row transition elements are listed below with their atomic number. Which one of them is expected to have the highest third ionisation enthalpy ?

Options

A. Vanadium (Z=23)
B. Chromium (Z=24)
C. Iron(Z=26)
D. Manganese (Z=25)

Answer

D

Explanation

In `._(23)V=1s^(2),2s^(2),2p^(6),3s^(2)3p^(6)3d^(3),4s^(2)`
Third electron which is removed in third ionisation potential belongs to `3d^(3)` -subshell. `._(24)Cr=1s^(2),2s^(2),2p^(6),3s^(2),3p^(6)3d^(5),4s^(1)`
third electron which is removed in thired ionisation potential belongs to `3d^(3)`-subshell. `._(26)Fe=1s^(2),2s^(2),2p^(6),3s^(2),3p^(6),3d^(6),4s^(2)`
Third electron which is removed in third ionisation potantial belong to `3d^(6)`-subshell
`._(25)Mn=1s^(2),2s^(2),2p^(6),3s^(2),3p^(6),3d^(5),4s^(2)`
Third electron which is removed in third ionisation potential belongs to `3d^(5)`-subshell. In all elements shell and subshell are same . Required amount of energy (enthalpy) is based upon the stability in an ion because it is half-filled subshell (while other are incomplete). So , Mn shows highest third ionisation potential or enthalpy.