d
The cyano and hydroxo complexes are far more stable than those formed by halide ion. This is due to the fact that \(C N^{-}\) and \(O H^{-}\) are strong lewis bases (nucleophiles). Further \(\left[F e(O H)_{5}\right]^{-3}\) is not formed. hence most stable ion is \(\left[F e(C N)_{6}\right]^{-3}\)