$(P)\, Fe(CO)_5\,\,\, (Q)\,CO\,\,\, (R)\, H_3B \leftarrow CO\,\,\,(S)\, [Mn(CO)_5]^-$
Correct sequence of $CO$ bond order:
$\underset{(CO\,bond\,order\,>\,3.0)}{\mathop{{{H}_{3}}B\leftarrow CO}}\,>\underset{B.O.=3.0}{\mathop{CO}}\,>\underset{CO\,bond\,order\,<3.0}{\mathop{Fe{{(CO)}_{5}}}}\,>\underset{(CO\,bond\,order\,<3.0)}{\mathop{{{[Mn{{(CO)}_{5}}]}^{-}}}}\,$