A base (alkaline substance) turns red litmus paper blue.
Explanation:
- Litmus is a natural indicator used to test whether a substance is acidic or basic
- Red litmus → turns blue in a base
- Blue litmus → turns red in an acid
Examples of Substances That Turn Red Litmus Blue:
- Sodium hydroxide (NaOH)
- Potassium hydroxide (KOH)
- Ammonium hydroxide (NH₄OH)
- Soap solution
Key Insight:
- Bases release OH⁻ (hydroxide ions) in aqueous solution
- These ions are responsible for the color change
Conclusion:
Any basic substance will turn red litmus blue, indicating its alkaline nature.