[Co(NH₃)₆]Cl₂

Co²⁺ : [Ar]3d⁷4s⁰4p⁰

For this complex ₀ < P.E., so pairing of electron does not take place.

sp³d² hybridisation

Total 3 unpaired electrons are present.

[Co(NH₃)₆]Cl₃

Co³⁺ : [Ar]3d⁶ 4s⁰ 4p⁰

d²sp³ hybridistion

NH₃ acts as SFL because ₀ > P.E.

So, here all electrons becomes paired.