(a) Complete the following equations:
(i) Cr₂O₇²⁻ + 2OH⁻ →
(ii) MnO₄⁻ + 4H⁺ + 3e⁻ →
(b) Account for the following:
(i) Zn is not considered as a transition element.
(ii) Transition metals form a larger number of complexes.
(iii) The E⁰ value for the Mn³⁺/Mn²⁺ couple is much more positive than that for Cr³⁺/Cr²⁺ couple.

(a) The balanced chemical equation :
(i) Cr₂O₇²⁻ + 2OH⁻ → 2CrO₄²⁻ + H₂O
(ii) MnO₄⁻ + 4H⁺ + 3e⁻ → MnO₂ + 2H₂O
(b)
(i) Zinc has the stable filled valence shell d¹⁰ electronic configuration in its ground state as well as in its most common oxidation state of +2. Hence, it is not considered as a transition element
(ii) Ions formed by transition metals have small sizes and high ionic charges. They possess vacant d-orbitals to accommodate lone pairs of electrons for bond formation. As a result transition metals forms a large number of complexes
(iii) The E⁰ value for the Mn³⁺/Mn²⁺ couple is more positive than that for Cr³⁺/Cr²⁺ couple. This is because Mn²⁺ ion is particularly stable due to extra stability of its half filled valence electronic configuration (d⁵). Thus Mn³⁺ ion has a very high tendency to gain an electron and form the much more stable Mn²⁺ ion.