Here's why:
* Nitric acid (HNO₃) is a strong acid. This means it readily releases hydrogen ions (H⁺) in solution.
* Litmus paper is an indicator. It contains a dye that changes color depending on the pH of the solution.
* Blue litmus paper is basic (alkaline). It turns red in acidic solutions.
Therefore, when blue litmus paper is dipped in dilute nitric acid, the hydrogen ions from the acid react with the dye in the litmus paper, causing it to change color from blue to red.
