Which one of the following can be used as an acid base indicator by a visually impaired student?

Options

A. Litmus
B. Turmeric
C. Vanilla essence
D. Petunia leaves

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question:**
The question asks which acid-base indicator can be used by a visually impaired student. This means we need to find an indicator that does not rely on visual cues (like color changes) but rather on other senses.

2. **Identifying Types of Indicators:**
There are two main types of indicators:
- **Visual indicators** (like litmus paper and turmeric) that change color in response to pH changes.
- **Olfactory indicators** that can be detected by smell.

3. **Recognizing Olfactory Indicators:**
Since the student is visually impaired, olfactory indicators are the best choice. These indicators change their smell in response to acidic or basic conditions.

4. **Example of an Olfactory Indicator:**
One well-known olfactory indicator is **vanilla extract**. It has a distinct smell that can be used to identify whether a solution is acidic or basic.

5. **How Vanilla Extract Works:**
- When vanilla extract is added to an **acidic solution** (like hydrochloric acid), its characteristic smell remains intact.
- When added to a **basic solution** (like sodium hydroxide), the smell of vanilla extract diminishes or disappears.

6. **Conclusion:**
Therefore, a visually impaired student can use vanilla extract as an olfactory indicator to determine the presence of an acid or a base. The answer to the question is that **vanilla extract** can be used as an acid-base indicator.

**Final Answer:**
The correct answer is **vanilla extract**.

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