The metal which does not form a polynuclear carbonyl is

Which of the following statements is incorrect?
$(1)$ $Al_4C_3$ is an organometallic compound.
$(2)$ Metal carbonyls are organometallic compounds.
$(3)$ $TEL$ (Tetraethyl lead) is a $\pi$-bonded organometallic compound.
$(4)$ Frankland reagent is a $\sigma$-bonded organometallic compound.

In which of the following compounds does iron have the lowest oxidation state?

The $C-O$ bond distance in $[V(CO)_6]$ and $[V(CO)_6]^-$ are:

Which of the following is not an organometallic compound?

The $\pi$-bonded organometallic compound which has ethene as one of its components is