Answer the question on basis of passage given below:
Chloroform is a very useful solvent for oils, fats and waxes and many organic compounds. It can also be used for preserving biological specimens. Chloroform was used as a general anaesthetic in surgery for a long time but because of its toxic nature, it is no longer used these days.
Why is chloroform stored in dark coloured air tight bottles?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Chloroform reacts with oxygen in presence of sun light.
Chloroform is slowly oxidised by air (oxygen) in the presence of light to carbonyl chloride, an extremely poisonous gas also known as phosgene:
\( \ce{2CHCl3 + O2} \xrightarrow{\text{light}} \ce{2COCl2 + 2HCl} \)
Both oxygen and light are needed for this reaction.
Why the other options are incorrect
Option (1) Chloroform reacts with oxygen only. — Incorrect. Oxygen alone does not oxidise chloroform at a useful rate; light is also needed, which is why the bottle is coloured.
Option (2) Chloroform reacts with sunlight. — Incorrect. Light alone does not form phosgene; oxygen of the air is the oxidising agent, which is why the bottle is filled and air tight.
Option (4) Chloroform reacts with carbon dioxide in presence of sunlight. — Incorrect. Carbon dioxide is not involved; the reaction is with oxygen.
NCERT (2026-27 edition):
Trichloromethane (Chloroform) – “Chloroform is slowly oxidised by air in the presence of light to an extremely poisonous gas, carbonyl chloride, also known as phosgene. It is therefore stored in closed dark coloured bottles completely filled so that air is kept out.”