Give the order of chelating effect of following ligands:

$\text{ (P) }{\mathrm{C}}_2{\mathrm{O}}_4^{2-}$   $\text{ (Q) }{\mathrm{EDTA}}^{4-}$

$\left(\mathrm{R}\right) \mathrm{dien}$

Since the quantity of bonds increases along with the amount of donor atoms, the correct order of chelating effect.
${\mathrm{EDTA}}^{+}>\text{dien }>{\mathrm{C}}_2{\mathrm{O}}_4^{2-}$
 Hence, option C is correct.