Question

Here, CO is a stronger ligand than $C{{l}^{-}}$ because:
A. CO is a neutral molecule
B. CO has$\pi $- bonds
C. CO is poisonous
D. CO is more reactive

Answer 1

Hint: A ligand is a molecule that gets attached to a metal atom and forms a complex. Ligands can be termed as stronger and weaker. A strong ligand is able to pair the electrons due to large splitting in the d – orbital, while weak ligands do not pair up the electrons as they have less splitting. This can be explained by crystal field splitting.

Complete answer:
A ligand is a molecule or an atom that attaches with a metal atom and forms a complex. Ligands can be classified as strong and weak according to the type of bonds present in it that is able to create large or low splitting of the d orbitals.
CO is considered as a stronger ligand than $C{{l}^{-}}$. The CO ligand is made up of carbon and oxygen having triple bonds as $C\equiv O$ this triple bond in CO marks the presence of 2 pi bonds. CO is a ligand that has vacant pi orbitals that creates a large extent of splitting in the d orbitals of the metal atom, this makes them a strong ligand.
So, CO has $\pi $- bonds that makes it a strong ligand due to more splitting.

So option B is correct.

Note:
The chloride ligand is not able to produce much splitting of the d orbital, one reason is that it has only a negative charge, while CO contains a positive as well as negative charge. Strong ligands are able to pair the electrons so they make low spin complexes while weak ligands do not pair up the electrons and make high spin complexes.