(i) In case of actinoids 5f orbitlas are filled while in lanthnoid series 4f orbitals are filled. The 5f orbitals exhibit a poorer shielding effect than 4f orbitals. So the electrons in 5f orbitals experience more force of nuclear pull than 4f electrons, thereby holding the outermost electrons more strongly, reducing the size of the atom, hence the greater contraction of actinoids than lanthanoids.
(ii) Colour is exhibited when electrons absorb energy in the visible region to jump to higher energy orbitals. In transitions metals the d-orbital electrons come in contact with ligands they split into different sets of orbitals. The electrons occupying the lower energy orbitals jump to the higher energy set. The energy difference between the sets is low and falls in the visible region. Hence we see the complementary colour to the energy transitions metals the d-orbital electrons come in contact with ligands they split into sets of orbitals.
Oxidation state of manganese in is +7 and that of is +3. These species undergo redox reaction in acidic medium to give reduced manganese in +2 oxidation state and an oxidised nitrate ion with nitrogen in +5 oxidation state.
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