Which process represents the change
Ti + 2I₂ → TiI₄ → Ti + 2I₂

van Arkel method very useful for removing all the oxygen and nitrogen present in the form of impurity in certain metals like zirconium and titanium. The crude metal is heated in an evacuated vessel with iodine. Then volatile metal iodide is formed. The metal iodide is decomposed on a tungsten filament by heating electrically to about 1800K. The pure metal is thus deposited on the filament by heating electrically to about 1800K. The pure metal is thus deposited on the filament.

$$\begin{gathered} \mathrm{Zr}+2{\mathrm{I}}_2\to {\mathrm{ZrI}}_4 \to \mathrm{Zr} + 2{\mathrm{I}}_2 \\ \mathrm{Ti}+2{\mathrm{I}}_2\to {\mathrm{TiI}}_4\to \mathrm{Ti}+2{\mathrm{I}}_2 \end{gathered}$$