Which of the following is not a $\pi -$ bonded organometallic complex?

The bond length of the $C-O$ bond in carbon monoxide is $1.128 \ \mathring{A}$. The $C-O$ bond length in $Fe(CO)_5$ is ............. $\mathring{A}$.

Which of the following is a $\pi$-complex?

The Wilkinson catalyst is

The number of bridged $CO$ ligands present in $Fe_2(CO)_9$ and $Co_2(CO)_8$,respectively are

The correct statement$(s)$ regarding the binary transition metal carbonyl compounds is (are) (Atomic numbers: $Fe = 26, Ni = 28$)
$A$. Total number of valence shell electrons at metal centre in $Fe(CO)_5$ or $Ni(CO)_4$ is $16$
$B$. These are predominantly low spin in nature
$C$. Metal-carbon bond strengthens when the oxidation state of the metal is lowered
$D$. The carbonyl $C-O$ bond weakens when the oxidation state of the metal is increased