Which of the following is a $\sigma$ and $\pi$ bonded organometallic compound?

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

What type of bonding is present in the $Fe-C$ bond of $Fe(CO)_5$?

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

The complex compounds which result from the coordination of carbon monoxide are known as