The compound which oxidizes slowly in the presence of air to give extremely poisonous phosgene gas is
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Chloroform
Chloroform (trichloromethane) is slowly oxidised by air in the presence of light to carbonyl chloride, the extremely poisonous gas phosgene:
\( \displaystyle \ce{2CHCl3 + O2} \xrightarrow{\text{light}} \ce{2COCl2 + 2HCl} \)
A little ethanol is added to stored chloroform; it converts any phosgene formed into harmless diethyl carbonate.
Why the other options are incorrect
Option (1) Dichloromethane — Incorrect. It is used as a solvent, paint remover and aerosol propellant; it is harmful to the nervous system but is not oxidised by air to phosgene.
Option (3) Carbon tetrachloride — Incorrect. It has no C–H bond to be oxidised in this way; it is used to make refrigerants and was used in fire extinguishers, and it depletes the ozone layer.
Option (4) Iodomethane — Incorrect. It contains no chlorine, so it cannot give carbonyl chloride; it is used as a methylating agent.
NCERT (2026-27 edition):
Trichloromethane (Chloroform)
