​Identify the series showing isolobal analogy.

A. $$CH_3, [Fe(CO)_5]^+$$​

B. $$CH^+_3,[Cr(CO)_5]^-$$​

C. $$CH_3^+,Ni(CO)_3$$​

D. $$CH^+,CpCo$$​

Correct option is B

​In current terminology, the structurally analogous fragments are said to be isolobal, and the relationship is expressed by the symbol

​The origin of the name is the lobe-like shape of a hybrid orbital in a molecular fragment. Two fragments are isolobal if their highest energy orbitals have the same symmetry (such as the σ symmetry of the H1s and a Csp³ hybrid orbital), similar energies, and the same electron occupation (one in each case in H1s and Csp³). Table lists some selected isolobal fragments and the first line shows isolobal fragments with a single frontier orbital. The recognition of this family permits us to anticipate by analogy with H−H that molecules such as H₃C−CH₃ and (OC)₅Mn−CH₃ can be formed. The second line of Table lists some isolobal fragments with two frontier orbitals, and the third line lists some with three.

​Using the isolobal principle, one can relate clusters that contain fragments having analogous orbital properties. Some isolobal pairs of metal carbonyl and hydrocarbon fragments are:

i. CH₃: Carbon has four valence electrons
Three electrons are given by three H atoms. Total electrons:4+3=7
[Fe (CO)₅]⁺: Electronic configuration of Fe: [Ar] 3d⁶4s²
CO donates two electrons. Total electrons: 8+ (5×2)-1 = 17
Positive charge leads to removal of one electron. 

ii. [CH₃]⁺​: Carbon has four valence electrons
Three electrons are given by three H atoms. Total electrons: 4+3-1=6

[Cr(CO)₅]^-: Electronic configuration of Cr: [Ar] 3d⁵4s¹.

Total electrons: 6+(5×2)+1=17

Negative charge leads to addition of one electron.

​
iii. [CH₃]⁺​: Carbon has four valence electrons
Three electrons are given by three H atoms. Total electrons: 4+3-1=6

[Ni(CO)₃]: Electronic configuration of Ni :[Ar] 3d⁸4s²

Total electrons: 10+(3×2) = 16

iv. [CH]⁺:Carbon has four valence electrons

One electron is given by one H atom. Total electrons: 4+1-1=4

[Co(Cp)] : Electronic configuration of Co: [Ar] 3d⁷4s².

Cyclopentadienyl ligand (Cp:C₅H₅^-​) donates five electrons. Total electrons: 9+5=14