Question

The yellow colour of $HN{O_3}$ is due to the dissolution of nitrogen dioxide $(N{O_2})$.
A. True
B. False

Answer 1

The chemical compound $HN{O_3}$ represents nitric acid which is a strong monobasic and an equally strong oxidizing agent. Nitric acid is seldom present in its pure form without the presence of any contaminants and also has a tendency to decompose.

Complete answer:
Nitric acid is a strong mono protic acid that dissociates completely in water to give one mole of hydrogen ions and nitrate ions.
Nitric acid has a yellowish-brownish colour due to the presence of gaseous nitrogen oxides dissolved in it. The eminent nitrogen oxide which imparts yellow colour to the otherwise colourless solution of nitric acid is nitrogen dioxide.
Nitrogen dioxide is a reddish brown gas that has high solubility in nitric acid and when dissolved in the colourless solution, it gives a yellow colour. The unstable solution of nitric acid has a tendency to get decomposed (without heating it). The decomposition produces nitrogen dioxide that remains dissolved in water. The decomposition reaction can be written as follows:
$4HN{O_3} \to 4N{O_2} + 2{H_2}O + {O_2}$
Hence, it is true that nitric acid appears to be yellow in colour due to the dissolution of nitrogen dioxide in it. So, option (A) is correct.

Note:
Pure and dilute nitric acid is a colourless solution. The nitric acid appears to be yellow only when a concentrated solution of nitric acid is allowed to stay standing still for long durations of time. The decomposition process that happens inside it makes it yellow.