Which one follow 18 electron octet rule?

Step-by-step solution

The 18 electron rule is used for predicting the stability and rationalizing the formula, especially organomettalic complexes. The number of valence electrons of the given species are as follows: [ Mn ( CO )₅ ]- Mn [ Ar ]₁₈ 3 ~d ^5 4 ~S ^2 =7 valence electrons [ Cr ( CO )₅ ]- Cr [ Ar ]₁₈ 3 ~d ^4 4 ~S ^2 =6 valence electrons [ Fe ( CO )₅ ]- Fe [ Ar ]₁₈ 3 ~d ^6 4 ~S ^2 =8 valence electrons [ Fe ( CO )₅ ] follow 18 electron octet rule.