Which of the following represents a chelating ligand?

Which of the following ligands forms a chelate?

The formula of alum is

An excess of $AgNO_3$ is added to $100 \ mL$ of a $0.05 \ M$ solution of tetraaquadichloridochromium$(III)$ chloride. The number of moles of $AgCl$ precipitated will be . . . . . . $\times 10^{-3}$. (Nearest integer)

Identify a ligand having two donor atoms but uses a pair of electrons of either donor atom to form a coordinate bond.

The coordination number and oxidation state of $Cr$ in $K_3[Cr(C_2O_4)_3]$ are respectively