Q.(a) Explain zone refining process with an example. OR

(a) Zone refining purifies a metal by repeatedly sweeping a narrow molten zone along a rod, concentrating impurities at one end. (b) Halogen oxidation states are found by balancing against oxygen's $-2$; the three reactions are standard $p$-block preparations/hydrolyses.

(a) Zone refining: This technique is used to obtain ultra-pure metals (especially semiconductor-grade Ge, Si, Ga) by exploiting the fact that impurities are more soluble in the molten form of the metal than in the solid form. A circular mobile heater is fitted around one end of an impure metal rod, creating a narrow molten zone; as the heater is slowly moved along the length of the rod, the molten zone also moves, and impurities dissolved in the melt are 'swept along' with it toward one end of the rod (since freshly solidifying metal behind the moving zone is purer, rejecting impurities into the still-molten region ahead). Repeating the pass several times progressively concentrates all the impurities at one end of the rod, which is then cut off, leaving an extremely pure metal at the other end. This is the standard method for purifying silicon and germanium to the extreme purity (99.999%+) required for semiconductor devices.

(b)(i) Oxidation states of the halogen:

• In $OF_2$: fluorine is more electronegative than oxygen, so F is assigned $-1$ (its usual state) and O is $+2$ here (unusual, but forced by F's higher electronegativity). Oxidation state of F = $-1$.
• In $I_2O_4$: treating oxygen as $-2$ (standard), total O charge $=4\times(-2)=-8$; for the neutral compound, total I charge $=+8$, so per iodine atom, oxidation state $=+8/2=+4$.

(b)(ii) Reactions: …