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 storage of chloroform is a problem?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Chloroform gets oxidised to highly poisonous gas phosgene in the presence of oxygen
On standing in air and light, chloroform is slowly oxidised by oxygen to carbonyl chloride (phosgene), an extremely poisonous gas:
\( \ce{2CHCl3 + O2} \xrightarrow{\text{light}} \ce{2COCl2 + 2HCl} \)
Carbon goes from +2 in \( \ce{CHCl3} \) to +4 in \( \ce{COCl2} \), so this is an oxidation. That is the storage problem; it is solved by keeping chloroform in closed, completely filled, dark coloured bottles.
Why the other options are incorrect
Option (2) Chloroform gets reduced to the highly poisonous gas, phosgene. — Incorrect. Phosgene is formed by oxidation, not reduction (the oxidation state of carbon rises from +2 to +4).
Option (3) Chloroform gets both oxidised followed by reduction to highly poisonous gas phosgene. — Incorrect. There is no reduction step; a single oxidation by air gives phosgene.
Option (4) Chloroform gets oxidised to form chlorine and HCl — Incorrect. Oxygen replaces the H–C hydrogen with a C=O group; the hydrogen leaves with one chlorine as HCl and the other two chlorines stay on carbon in \( \ce{COCl2} \), so no free chlorine is released.
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.”