Question

Nitric acid in its pure state is colorless but laboratory Nitric acid is slightly yellow or brown due to dissolved

• A. Chlorine
• B. Nitrogen monoxide
• C. Nitrogen dioxide
• D. None of these

Answer 1

The correct option is C

Nitrogen dioxide

Explanation for correct option (c): Nitrogen dioxide

1. The dissolution of Nitrogen dioxide in Nitric acid causes the change of yellow or brown color.
2. The chemical reaction is as follows:
   $\underset{(\mathrm{Nitric}\mathrm{acid})}{4{\mathrm{HNO}}_3\left(\mathrm{l}\right)}\stackrel{∆}{\to }\underset{\left(\mathrm{Water}\right)}{2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}+\underset{(\mathrm{Yellow}-\mathrm{brown})}{\underset{(\mathrm{Nitrogen}\mathrm{dioxide})}{4{\mathrm{NO}}_2\left(\mathrm{g}\right)}}+\underset{\left(\mathrm{Ox}y\mathrm{gen}\right)}{{\mathrm{O}}_2\left(\mathrm{g}\right)}$
3. Due to thermal decomposition, Nitric acid changes to Nitrogen dioxide, which is yellow-brown in color.
4. Now it is clear that Nitric acid in its pure state is colorless but in laboratory Nitric acid is slightly yellow or brown due to dissolved Nitrogen dioxide. Hence, option C is correct.