Eriochrome black T (EBT) is an indicator in titrimetric estimation of calcium at pH 10.0 giving pink colour to the solution. It has the structure shown below, with $$pK_{a2} = 6.3$$ and $$pK_{a3} = 11.5$$. Considering that the pH of solution is 10.0, which statement or statements describe the complexation of EBT with Ca(II) correctly?

On dissociation of EBT, Ca(II) binds at $$\text{SO}_3^-$$ to form a 1 to 2 complex

Both sulphonate and nitro groups are involved in 1 to 1 complexation with Ca(II)

EBT acts as a bidentate ligand to form a dianionic species, with deprotonation of one $$-\text{OH}$$ group, where Ca(II) binds to azo nitrogen and phenolic oxygen trans to the $$-\text{NO}_2$$ group in a 1 to 2 ratio

There is a mixture of complexes of Ca(II) with EBT acting as a bidentate and tridentate ligand