Litmus paper turns blue when dipped in a/an:

Litmus paper is a common acid-base indicator used to determine if a solution is acidic, basic, or neutral. 1. **Acidic Solutions:** In an acidic solution (where $pH < 7$), blue litmus paper turns red, and red litmus paper remains red. 2. **Basic Solutions:** In a basic (alkaline) solution (where $pH > 7$), red litmus paper turns blue, and blue litmus paper remains blue. 3. **Neutral Solutions:** In neutral solutions like pure water or salt solutions ($pH \approx 7$), litmus paper generally does not change its existing color. Since the question states the litmus paper turns **blue**, the solution must be a **Basic solution**.