Question

Which of the following is a $\pi$ - acceptor ligand?

• A. $N{H}_3$
• B. $CO$
• C. $F^{-}$
• D. Ethylene diamine

Answer 1

Answer: (B)

$CO$

A pi bond ligand or a pi acid ligand is one which gives electron to central atom through coordination bond but also accepts electron in the form of a partial pi bond from central atom(from its anti bonding orbital).

Since now carbon is forming one full bond and one partial bond with central atom its bond order with oxygen decreases and hence bond length increases

Option B is correct.