The oxidation number of iron in the compound formed during the brown ring test for $NO_3^{-}$ ion is . . . . . .

The complex of $Ni^{2+}$ ion and dimethylglyoxime contains $..........$ number of Hydrogen $(H)$ atoms.

The coordination number of $Fe(II)$ in oxyhemoglobin is ..........

$A$ complex has a composition corresponding to the formula $CoBr_2Cl \cdot 4NH_3$. What is the structural formula if conductance measurements show two ions per formula unit? Silver nitrate solution gives an immediate precipitate of $AgCl$ but no $AgBr$.

Potassium ferrocyanide is a

$EDTA$ (Ethylenediaminetetraacetate ion) is a hexadentate ligand. Identify the number of donor atoms in an $EDTA$ molecule that form coordinate bonds with a central metal atom or ion in a complex.