Which chemical changes the color of nitric acid?

Answer 1

Nitric acid in its pure form is colorless. The color changes to brownish-yellow due to the presence of nitrogen dioxide (NO2). This nitrogen dioxide usually forms when bottles containing nitric acids are not properly capped. Nitric acid reacts with oxygen in the air to form nitrogen dioxide which remains dissolved in the acid to give this particular color.

Answer 2

Nitric acid itself is colorless. However, exposure to light and air can cause it to undergo decomposition, leading to the formation of nitrogen oxides which can impart a yellow or brown color to the solution.