Freshly prepared aniline is usually colourless, but it becomes coloured on storage. Which of the following is the reason?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Atmospheric oxidation
Aniline and other arylamines are slowly oxidised by the oxygen of the air. The oxidation products are coloured, so a stored sample turns coloured.
NCERT (2026-27 edition):
9.5 Physical Properties – “…Aniline and other arylamines are usually colourless but get coloured on storage due to atmospheric oxidation.”