The liquid which causes formation of poisonous gas when exposed to sunlight in presence of air or oxygen \((O_2)\) is:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → CHCl3
Chloroform (trichloromethane) is slowly oxidised by air in the presence of light to an extremely poisonous gas, carbonyl chloride (phosgene):
\( \ce{2CHCl3 + O2} \xrightarrow{\ce{light}} \ce{2COCl2 + 2HCl} \)
For this reason chloroform is stored in closed, dark coloured bottles, completely filled, so that air is kept out.
Why the other options are incorrect
Option (1) CHF2–CHF2 — Incorrect. A hydrofluorocarbon; C–F bonds are very strong and it is not oxidised by air in light to a poisonous gas.
Option (3) CCl4 — Incorrect. It has no C–H bond to be oxidised in this way; it is used as a solvent and is known for damaging the ozone layer when it reaches the upper atmosphere.
Option (4) CF4 — Incorrect. Tetrafluoromethane is a gas at room temperature, not a liquid. It has no C–H bond to be oxidised, and its strong C–F bonds make it very inert.
NCERT (2026-27 edition):
Trichloromethane (Chloroform)
