Question

why nitric acid is pale yellow in colour

Answer 1

1. Due to thermal decomposition of HNO₃,i.e.,nitric acid,NO₂ is produced.
2. The reaction is as follows :

4HNO₃ $\to$ 2 H₂O + 4 NO₂ + O₂

3. This NO₂,nitrogen dioxide,is reddish brown in colour and when mixed with HNO_​3 imparts pale yellow colouration to it.