Question

Sum of the paired electrons present in the orbital with l=2 in all the species Fe²⁺, Co²⁺ and Ni²⁺ are

2nd one

Comments

Is it 15 Allen has given 12

Answer 1

 l = 2 means d orbitals 

electronic configuration of Fe2+ = [Ar] 3d6 

six electrons in d orbitals 4 will be unpaired 2 will be paired 

electronic configuration of Co2+ = [Ar] 3d7 

three electrons will be unpaired four will be paierd 

electronic configuration of Ni2+ = [Ar] 3d8 
two electrons will be unpaired and six will be paired

So the sum of paired electrons is 2+4+6=12