Chlorine is extracted from brine by:

The correct answer is Option (1) → Oxidation

Elements that occur as anions are extracted by oxidation, since the anion must lose electrons to become the element. Chlorine occurs in brine (concentrated aqueous NaCl) as \( \ce{Cl^{-}} \) ions, which are oxidised to \( \ce{Cl2} \):

    \( \ce{2Cl- -> Cl2 + 2e-} \)

The reaction is not spontaneous, so it is carried out by electrolysis with an external e.m.f..

\( \ce{Cl2} \) is set free at the anode, the electrode where oxidation takes place. So chlorine is extracted from brine by oxidation.

Why the other options are incorrect

• Option (2) Leaching — Incorrect. A method of concentrating an ore by dissolving it in a suitable reagent (bauxite in NaOH, silver and gold in NaCN); it does not change \( \ce{Cl^{-}} \) into \( \ce{Cl2} \).

• Option (3) Distillation — Incorrect. A refining method for low-boiling metals such as zinc and mercury; it separates substances, it does not oxidise them.

• Option (4) Reduction — Incorrect. Used to obtain metals from their oxides or cations (gain of electrons); chlorine in brine has to lose electrons.

NCERT (Pre-rationalised edition, 2022-23):
Oxidation Reduction – “Besides reductions, some extractions are based on oxidation particularly for non-metals. A very common example of extraction based on oxidation is the extraction of chlorine from brine (chlorine is abundant in sea water as common salt).
    2Cl^–(aq) + 2H₂O(l) → 2OH^–(aq) + H₂(g) + Cl₂(g)
The ΔG^o for this reaction is + 422 kJ. When it is converted to E^o (using ΔG^o = – nE^oF), we get E^o = – 2.2 V. Naturally, it will require an external e.m.f. that is greater than 2.2 V.”