Inert pair effect: why TlI₃ is really Tl⁺I₃⁻; and why the chelate effect is an entropy effect

(a) What is the inert pair effect? Using $E^\circ(\ce{Tl^3+/Tl+}) = +1.25$ V and $E^\circ(\ce{I3-/I-}) = +0.54$ V, show that thallium(III) iodide, TlI₃, is really thallium(I) triiodide, $\ce{Tl+I3-}$. Give one other example of the effect. (5 marks)
(b) At 298 K, for $\ce{Cd^2+(aq) + 4CH3NH2}$: $\Delta H^\circ = -57.3$ kJ mol⁻¹, $\Delta S^\circ = -67.3$ J K⁻¹ mol⁻¹; for $\ce{Cd^2+(aq) + 2en}$: $\Delta H^\circ = -56.5$ kJ mol⁻¹, $\Delta S^\circ = +14.1$ J K⁻¹ mol⁻¹. Calculate $\Delta G^\circ$ and $\log\beta$ for each and explain the chelate effect. (5 marks)