Which of the following acts as a bidentate ligand in complex formation?

Which one of the following forms a complex with an excess of $CN^{-}$ (cyanide) having a coordination number of two?

Which of the following is a neutral ligand?

The coordination numbers of $Fe$ in the complexes $[Fe(CN)_6]^{4-}$,$[Fe(CN)_6]^{3-}$,and $[FeCl_4]^{-}$ are respectively:

The coordination number and the oxidation state of the element $E$ in the complex $[E(en)_2(C_2O_4)]NO_2$ (where $en$ is ethylene diamine) are,respectively:

$A$ complex compound of $Co^{3+}$ with molecular formula $CoCl_{x} \cdot yNH_3$ gives a total of $3$ ions when dissolved in water. How many $Cl^{-}$ ions satisfy both primary and secondary valencies in this complex?