Question

Second ionisation energy of cr is higher than vn and mn why?

Answer 1

When Cr⁺ is formed the specie became more stable by acquiring the configuration  [Ar] 3d⁵, 4s⁰ Thus its second ionization energy is higher.

It can  by better understand by considering the electronic configuration of Cr.

The electronic configuration of Cr is,

Cr = [Ar] 3d⁵, 4s¹

It form ion by removing the one electron of 4s. Thus it form Cr⁺.

When Cr⁺ is formed the electronic configuration became,

Cr = [Ar] 3d⁵, 4s⁰

Here we can see there are 5 electrons in 3d which is the more stable state and required highest energy to remove the second electron from Cr. Thus its second ionization energy is higher.