$A$ ligand is a

Which molecule/ion among the following cannot act as a ligand in complex compounds?

$3$ moles of a metal complex with the formula $Co(en)_2 Cl_3$ gives $3$ moles of silver chloride on treatment with an excess of silver nitrate. The secondary valency of $Co$ in the complex is $.....$ (Round off to the nearest integer).

The mass of carbon present in $0.5 \, mol$ of $K_4[Fe(CN)_6]$ is .............. $g$.

Write a note on ambidentate ligands.

The types of bonds present in ${K_4}[Fe(CN)_6]$ are: