Question

Give reason for the following:

Nitric oxide becomes brown when released in air.

Answer 1

1. Nitric oxide (NO) is a colourless gas when pure.
2. When released in air, it reacts with oxygen (O₂).
3. This reaction forms nitrogen dioxide (NO₂), which is brown in colour.
4. The formation of NO₂ causes the brown colour to appear.
5. The overall reaction is: 
   \[\ce{2NO + O2 -> \underset{(brown gas)}{2NO2}}\]

Thus, nitric oxide appears brown due to the formation of brown nitrogen dioxide on exposure to air.