a.Write the formula of the following coordination compound ?
Iron (III) hexacyanoferrate (II)
b. What type of isomerism is exhibited by the complex [Co(NH₃)₅Cl]SO₄.

a. The formula of the complex anion hexacyanoferrate (II) is [Fe (CN)₆​] ⁻⁴. The oxidation number of iron is +2 and each cyanide ion has −1 charge. Hence, the net charge on the complex anion is +2+6(−1) =−4.
-4 charge on complex anion will be balanced by +3 charge on Fe³⁺ cation when 4 Fe³⁺ cations combine with 3 [Fe (CN)₆​] ⁻⁴ complex anions.
 The formula of the coordination compound Iron (III) hexacyanoferrate (II) is Fe₄([Fe (CN)₆​])₃​
Note: In the name Iron (III) hexacyanoferrate (II), the numbers in parenthesis in roman numerals indicates the oxidation number of iron atoms.

b. Ionization Isomerism

Compounds made of same element and having same composition but give different ions in solution are called ionization isomers. These isomers are formed by the interchange of the position of ligands inside and outside the coordination sphere. Such isomers can be detected by conductance measurements or by chemical tests.
In aqueous solution, [Co (NH₃​)₅​Cl]SO₄​ gives sulphate ions and [Co (NH₃​)₅​SO₄​Cl] gives chloride ions. Thus, [Co (NH₃​)₅​Cl]SO₄​ and [Co (NH₃​)₅​SO₄​] Cl represents ionization isomers.