Correct sequence of CO bond order in given compounds is :
(P) Fe(Co)₅ (Q) Co (R) H₃B $\leftarrow$CO (S) [Mn(Co)₅]^-

$\text{ CO bond order }\propto \frac{1}{\text{ Extent of back bonding }(\mathrm{M}\to \text{ CO })}$
Correct sequence of CO bond order :
$\underset{\text{ (CO bond order }>3.0\text{ ) }}{{\mathrm{H}}_3\mathrm{B}}{\mathrm{CO}}_{\text{B.O. }=3.0}{\mathrm{CO}}_{\text{CO bond order }<3.0}>\mathrm{Fe}(\mathrm{CO}{)}_{\text{(CO bond order }<3.0\text{ ) }}$