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Chemistry Question on d -and f -Block Elements

The atomic number of V, Cr, Mn and Fe are respectively 23, 24, 25 and 26.Which one of these may be expected to have the highest second ionisation enthalpy ?

A

V

B

Cr

C

Mn

D

Fe

Answer

Cr

Explanation

Solution

Outer electronic configurations of V, Cr, Mn and Fe are as follows. V(4s23d3),Cr(4s13d5),Mn(4s23d5),Fe(4s23d6)V(4s^2 3d^3), Cr(4s^1 3d^5), Mn(4s^23d^5), Fe(4s^23d^6) Outer electronic configuration of uni-positive ions are V+(4s13d3),Cr+(3d5),Mn+(4s13d5),Fe+(4s13d6)V^+(4s^13d^3), Cr^+ (3d^5), Mn^+(4s^13d^5), Fe^+ (4s^13d^6) Clearly, I.E2E_2 of Cr will be highest as Cr+Cr^+ has exactly half filled dd-subshell.