The correct sequence of $CO$ bond order in the given compounds is:
$(P) \ Fe(CO)_5, (Q) \ CO, (R) \ H_3B \leftarrow CO, (S) \ [Mn(CO)_5]^-$

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

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A)$: The metal-carbon bond in metal carbonyls possesses both $\sigma$ and $\pi$ character.
Reason $(R)$: The ligand-to-metal bond is a $\sigma$ bond and metal-to-ligand bond is a $\pi$ bond.
In the light of the above statements,choose the most appropriate answer from the options given below :

In $Fe_2(CO)_9$,the two iron atoms are

Which of the following does not have a metal-carbon bond?

Finely divided iron combines with $CO$ to give