Question

Which of the following oxides of nitrogen is a coloured gas?
A.${N_2}O$
B. $NO$
C. ${N_2}{O_4}$
D. $N{O_2}$

Answer 1

The unpaired electrons present in the molecular orbital shows that the compound is paramagnetic. The paramagnetic nature is responsible for the coloured nature of the oxide. At low temperature the nitrogen dioxide diminishes to form a colorless oxide.

Complete step by step answer:
A. ${N_2}O$ is chemically named as nitrous oxide. The nitrous oxide is also known as laughing gas or nitrous. It is an oxide of nitrogen. It is a colorless gas with non-flammable properties. It has a metallic scent and taste. The nitrous oxide acts as an oxidizing agent.
B. NO is chemically named as nitric oxide or nitrogen oxide. The nitric oxide is one of the principal oxide of nitrogen. It is a colorless gas. The nitric oxide acts as a free radical due to the presence of lone pairs of electrons.
C. ${N_2}{O_4}$ is chemically known as dinitrogen tetroxide. It is a colorless gas. It forms an equilibrium mixture with nitrogen dioxide. Dinitrogen tetroxide is used as a powerful oxidizer. In this compound, two nitro groups are joined together.
D. $N{O_2}$ is chemically named as nitrogen dioxide. The nitrogen gas at higher temperature is a reddish brown gas. The nitrogen dioxide is paramagnetic in nature.
Thus, the oxides of nitrogen is a coloured gas is nitrogen dioxide.
Therefore, the correct option is D.

Note:
The reddish brown nitrogen dioxide becomes yellowish – brown liquid below 21 degree celsius and by lowering the temperature to 11.2 degree Celsius forms colorless dinitrogen tetroxide.