Out of given 3 complex

(I) [Mn(CO)6]+ (II) [Cr (CO)6] (III) [V(CO)6]-

(A) (III)has max. C-O length

(B) (II)has lowest O-N of metal

(C) (I)has min. no. of electrons

(D) (III)has min. pia-character in metal -carbon bond

The correct option is A

Reason:

Due to backbonding the CO bond order is affected, as we move from left to right across the periodic table the energy difference between d-π and π* orbitals increases and back bonding becomes difficult.

Hence C-O bond distance is maximum in (III) then (II) and then (I)