Which of the following compounds contains complex anions?

Identify the set which does not have ambidentate ligand$(s)$.

What is the coordination number of the central metal ion in $[Fe(C_2O_4)_3]^{3-}$?

The following reaction is performed for detection of $NO_2^{-}$: $FeSO_4 + NO \rightarrow$ Product. Choose the correct statement.

Which of the following molecules cannot act as a bidentate ligand?

Consider the following statements according to Werner's theory:
$1.$ Ligands are connected to the central metal ions by coordinate bonds.
$2.$ Secondary valencies have directional properties.
$3.$ Secondary valencies are non-ionisable.
Which of these statements are correct?