Which lichen is used for making litmus paper ?

Options

A. Roccella
B. Cetraria
C. Cladonia
D. Usnea

Answer

To determine which lichen is used for making litmus paper, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Litmus**: Litmus is a natural dye that is used to test the acidity or alkalinity of a solution. It changes color depending on the pH level: red in acidic conditions (pH < 4.5) and blue in alkaline conditions (pH > 8.5).

**Hint**: Remember that litmus paper is used for pH testing and changes color based on acidity or alkalinity.

2. **Identifying Sources of Litmus**: Litmus is primarily derived from certain species of lichens. Various lichens can produce this dye, but not all lichens are suitable for this purpose.

**Hint**: Focus on the lichens known for their dyeing properties.

3. **Evaluating the Options**: The options provided are:
- Rosella
- Citraria
- Cladonia
- Usnea

**Hint**: Consider the specific uses of each lichen mentioned in the options.

4. **Researching Each Lichen**:
- **Rosella (Rocella tinctoria)**: This is known for being a primary source of litmus dye.
- **Citraria**: Often used in traditional medicine for respiratory issues.
- **Cladonia**: Typically used for ornamental purposes.
- **Usnea**: Known for its medicinal properties, particularly in treating certain diseases.

**Hint**: Look for the lichen specifically associated with dye production.

5. **Conclusion**: Based on the information gathered, the lichen used for making litmus paper is **Rosella (Rocella tinctoria)**.

**Final Answer**: The correct answer is **Rosella**.