What colour do the following indicators turn when added to an acid?
Litmus solution

Answer

### Step-by-Step Solution:

1. **Understanding Litmus**: Litmus is a natural dye derived from lichens, used as an indicator to determine whether a solution is acidic or basic.

2. **Types of Litmus**: There are two types of litmus paper: red litmus and blue litmus.
- Red litmus paper is used to test for bases.
- Blue litmus paper is used to test for acids.

3. **Reaction of Litmus with Acids**:
- When red litmus paper is placed in an acidic solution, it **remains red**. This indicates that the solution is acidic.
- When blue litmus paper is placed in an acidic solution, it **turns red**. This indicates that the solution is acidic.

4. **Conclusion**:
- If you add an acid to red litmus, it stays red.
- If you add an acid to blue litmus, it changes to red.

### Final Answer:
- Red litmus solution remains red when added to an acid.
- Blue litmus solution turns red when added to an acid.