In $Fe(CO)_5$,the $Fe-C$ bond has

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

Which of the following are organometallic compounds? $(1)$ Grignard reagent $(2)$ Sodium methoxide $(3)$ Trimethylboron $(4)$ $Al_2(CH_3)_6$

The correct statements about metal carbonyls are:
$A$. The metal-carbon bonds in metal carbonyls possess both $\sigma$ and $\pi$-character.
$B$. Due to synergic bonding interactions between metal and $CO$ ligand, the metal-carbon bond becomes weak.
$C$. The metal-carbon $\sigma$ bond is formed by the donation of a lone pair of electrons on the carbonyl carbon into a vacant orbital of metal.
$D$. The metal-carbon $\pi$ bond is formed by the donation of electrons from a filled $d$-orbital of metal into a vacant $\pi^*$ orbital of $CO$.
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Match List-$I$ with List-$II$:

$LIST-I$ (Substances)	$LIST-II$ (Element Present)
$A$. Ziegler catalyst	$I$. Rhodium
$B$. Blood pigment	$II$. Cobalt
$C$. Wilkinson catalyst	$III$. Iron
$D$. Vitamin $B_{12}$	$IV$. Titanium

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