Name the acid-base indicator extracted from lichens.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for the name of an acid-base indicator that is extracted from lichens.

2. **Identifying Lichens**: Lichens are a symbiotic association between fungi and algae. They are known for their ability to thrive in various environments and are often used in various applications, including as natural dyes.

3. **Recognizing Acid-Base Indicators**: Acid-base indicators are substances that change color in response to changes in pH levels. They are commonly used in titrations and pH testing.

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