Question

The pair of ions having same electronic configuration is............
(a) Cr³⁺,Fe³⁺
(b) Fe³⁺,Mn²⁺
(c) Fe³⁺,Co³⁺
(d) Sc³⁺,Cr³⁺ 

Answer 1

(b) Cr³⁺ (Z=24)=[Ar]3d³
Fe³⁺ (Z=26) = [Ar]3d⁵
Mn²⁺(Z=25)=[Ar]3d⁵
Co³⁺(Z=27)=[Ar]3d⁶
Sc³⁺(Z=21)=[Ar]3d⁰
Fe³⁺ and Mn²⁺ will have the same number of electrons, i.e.,23 and, hence, have the same electronic configuration. 
  

Answer 2

Fe3+ and Mn2+ will have the same number of electrons, i.e.,23 and, hence, have the same electronic configuration.