(i) +3 / III «Mn is +3 and $\ce{H2O}$ is neutral, so each $\ce{C2O4}$ ligand carries a 2− charge: 2x + 4(−2) = −2» ✔

(ii) Any three of:

$\ce{Mn^3+}$ has a partially filled d-sublevel «3d$^4$» ✔

«the ligands cause» the d-orbitals «to» split into two sets of different energy ✔

light is absorbed as an electron is promoted from the lower to the higher set of d-orbitals «d-d transition» ✔

the energy gap corresponds to a wavelength in the visible region of the spectrum ✔

the colour observed «red-brown» is complementary to the colour of the light absorbed ✔

(iii) «the catalyst provides» an alternative reaction pathway / a different mechanism «involving $\ce{Mn^2+}$» ✔

with a lower activation energy «so a greater proportion of collisions are successful» ✔

(iv) Oxidation half-equation: $\ce{C2O4^2- -> 2CO2 + 2e-}$

Overall redox equation: $\ce{2Mn^3+ + C2O4^2- -> 2Mn^2+ + 2CO2}$

(v) products drawn lower in energy than the reactants ✔

intermediate drawn at an energy minimum between two maxima ✔

$E_\mathrm{a}$ marked for both steps «from the reactants and from the intermediate up to the respective maximum» ✔

$\Delta H$ marked from the reactants down to the products ✔

(i) [1]; do not accept 3 or 3+. (ii) [3 max] from the five points; the complementary-colour point scores only if absorption of light is mentioned. (iii) M1: alternative pathway or mechanism; M2: lower activation energy. (iv) M1: half-equation with the electrons on the right; M2: overall equation balanced for charge with 2Mn3+, ECF from M1. (v) [1] per feature; any relative peak heights are accepted and single-headed or double-headed arrows both score.