Which of the following is formed when $n$-butyl lithium reacts with tin$(II)$ chloride?

Which of the following compounds is not considered an organometallic compound?

The oxidation state of cobalt in the following molecule is

The Wilkinson catalyst is

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 $CO$.
Choose the correct answer from the options given below:

The sandwich structure of ferrocene was confirmed by which of the following?