Freon-12 from tetrachloromethane is synthesized by

The correct answer is Option (3) → Swarts reaction

In the Swarts reaction, an alkyl chloride or bromide is heated with a metallic fluoride such as AgF, \( \ce{Hg2F2} \), \( \ce{CoF2} \) or \( \ce{SbF3} \), and the chlorine or bromine is replaced by fluorine. It is the usual way of making alkyl fluorides.

Freon-12 is dichlorodifluoromethane, \( \ce{CCl2F2} \). It is made from tetrachloromethane by replacing two chlorine atoms with fluorine:

    \( \displaystyle \ce{3CCl4 + 2SbF3 -> 3CCl2F2 + 2SbCl3} \)

So Freon-12 is synthesised from tetrachloromethane by the Swarts reaction.

Why the other options are incorrect

• Option (1) Gattermann Reaction — Incorrect. A benzenediazonium salt is treated with copper powder and the halogen acid to give an aryl chloride or bromide; it starts from an aromatic diazonium salt, not from \( \ce{CCl4} \).

      \( \displaystyle \ce{C6H5N2^+Cl^-} \xrightarrow{\ce{Cu/HCl}} \ce{C6H5Cl + N2} \)

• Option (2) Hunsdiecker Reaction — Incorrect. The silver salt of a carboxylic acid is heated with bromine in \( \ce{CCl4} \) and gives an alkyl bromide with one carbon atom less; no fluorine is brought in.

      \( \displaystyle \ce{RCOOAg + Br2} \xrightarrow{\ce{CCl4}} \ce{R-Br + CO2 + AgBr} \)

• Option (4) Finkelstein Reaction — Incorrect. An alkyl chloride or bromide is heated with NaI in dry acetone to give an alkyl iodide, not a fluoride.

      \( \displaystyle \ce{R-Cl + NaI} \xrightarrow{\text{dry acetone}} \ce{R-I + NaCl} \)

NCERT (2026-27 edition):
Freons

Note: The same/similar question has been asked in different years by NTA as per the details given below: