Which of the following species can act as reducing agent ?

Mn(CO)₆ can act as reducing agent because the metal corbonyl is stable when EAN is equal to nearest noble gas configuration.
$\underset{\underset{\text{ EAN }=37}{\left[\text{ Less stable }\right)}}{\left[\mathrm{Mn}(\mathrm{CO}{)}_6\right]}\stackrel{-{\mathrm{e}}^{-}}{⟶}\left[\begin{array}{c}\mathrm{Mn}(\mathrm{CO}{)}_6\\ \text{ EAN }=36\\ \text{ (More stable) }\end{array}\right.$