(i) coordination «covalent» bond ✔

(ii) +3 ✔

(iii) Any three of:

iron(III) has a partially filled d-sublevel ✔

the ligands split the d-orbitals into two sets of different energy ✔

an electron is promoted from the lower set to the higher set by absorbing light ✔

the energy difference corresponds to a frequency in the visible region «and the light transmitted is the complementary colour of the light absorbed» ✔

(iv) $K = \dfrac{[\ce{[Fe(CN)6]^3-}]}{[\ce{Fe^3+}][\ce{CN-}]^6}$ ✔

$[\ce{CN-}] = 6 \times 4.00 \times 10^{-8} = 2.40 \times 10^{-7}$

$K = \dfrac{0.500}{4.00 \times 10^{-8} \times (2.40 \times 10^{-7})^6} = \dfrac{0.500}{4.00 \times 10^{-8} \times 1.91 \times 10^{-40}} = 6.5 \times 10^{46}$

(v) $E^\ominus$ for the complex couple, +0.36 V, is less positive than +0.77 V for $\ce{Fe^3+}/\ce{Fe^2+}$

the less positive the $E^\ominus$, the more readily the reduced form gives up electrons, so $\ce{[Fe(CN)6]^4-}$

(i) [1] coordination or dative covalent. (ii) [1] +3 or III; do not accept 3+ or 3. (iii) [3 max] one mark per marking point; the statement that the observed colour is complementary does not by itself earn the last mark. (iv) [3] M1 equilibrium expression; M2 [CN-] from the 1:6 stoichiometry; M3 value of K, accept 6.5 to 6.6 × 10^46; award [3] for a correct final answer. (v) [2] M1 comparison of the two E° values; M2 conclusion 'stronger reducing agent' with the reason.