$(A)$ In octahedral complex: $\left[ M \left( H _{2} O \right)_{6}\right]^{2+}$
$C.F.S.E.$ $=\left(-0.4 \Delta_{0}\right) \times 4+\left(+0.6 \Delta_{0}\right) \times 2+0 \times P$
$(B)$ In tetrahedral complex: $\left[ M \left( H _{2} O \right)_{4}\right]^{2+}$
$C.F.S.E.$ $=\left(-0.6 \Delta_{t}\right) \times 3+\left(+0.4 \Delta_{t}\right) \times 3+0 \times P$
$=-0.6 \Delta_{ t }$
$(A)$ $\left. Na _{4}\left[ Fe ( CN )_{5} NOS \right)\right]$
$(B)$ $Na _{4}\left[ FeO _{4}\right]$
$(C)$ $\left[ Fe _{2}( CO )_{9}\right]$