Which of the following has second ionisation potential less than expected

Options

A. Cr
B. Zn
C. V
D. Mo

Answer

B

Explanation

Second ionization potential of Zn is less than Cu because `Cu^(+)` is more stable than `Zn^(+)` as :
`Cu^(+) =[Ar] 3d^10 and Zn^(+) = [Ar] 3d^10 4s^1`
`Cu^(+)` has filled orbitals and has one less shell than `Zn^(+)`. So 2nd I.E. of Cu > Zn.