Which of the following species(s) act as reducing agent.

Because the metal carbonyl is stable when EAN is equal to the nearest noble gas configuration,  $\left[\mathrm{Mn}(\mathrm{CO}{)}_6\right]$ can act as a reducing agent.

$\begin{array}{lc}V(CO{)}_6+e^{-}& \to V(CO{)}_6^{-}\\ (O.A)& EAN=36\\ Mn(CO{)}_6\to & Mn(CO{)}_6^{+}+e^{-}\\ (\text{R.A.) }& \mathrm{EAN}=36\end{array}$

Thus, the correct answer is A, B, D.