Q.Which of the following is coloured ?

A species with an element in an intermediate oxidation state can be both oxidant and reductant. NO2 (N in +4) and H2O2 (O in -1) both fit. Correct option (b).

To act as both oxidant and reductant, an element must have an oxidation state between its minimum and maximum:

• NO2: nitrogen is +4 (between -3 and +5), so NO2 can be oxidised (to nitrate) or reduced (to NO/N2), acting as both.
• H2O2: oxygen is -1 (between -2 and 0), so H2O2 can be reduced to H2O (oxidant) or oxidised to O2 (reductant) - it is the classic example of a substance acting as both. …

Laughing gas is nitrous oxide, N2O; when inhaled in small amounts it produces hysterical laughter, hence the name.

The oxides of nitrogen and their names:

• Nitric oxide = NO
• Nitrous oxide = N2O — the anaesthetic "laughing gas"
• Dinitrogen trioxide = N2O3
• Dinitrogen pentoxide = N2O5 …

NO2 is a reddish-brown coloured gas; NH3, N2O and NO are colourless.

Nitrogen dioxide, NO2, is an odd-electron molecule that absorbs visible light and appears reddish-brown.

• NH3 (ammonia) is a colourless gas. …