The substances whose odour changes in acidic or basic media are called ______. Options are (a) Natural indicators (b) Synthetic indicators (c) Acid-base indicators (d) Olfactory indicators.

Options

A. Natural indicators
B. Synthetic indicators
C. Acid-base indicators
D. Olfactory indicators

Answer

To solve the question, we need to identify the correct term for substances whose odor changes in acidic or basic media. Let's analyze the options provided:

1. **Natural indicators**: These are substances derived from natural sources that can indicate pH changes, but they do not specifically refer to changes in odor.

2. **Synthetic indicators**: These are man-made substances that change color in response to pH changes. Again, they do not specifically refer to changes in odor.

3. **Acid-base indicators**: This term generally refers to substances that change color in response to acidity or basicity. While they indicate pH changes, they do not specifically relate to odor changes.

4. **Olfactory indicators**: These are substances whose odor changes when they are in acidic or basic environments. This matches the description given in the question.

Based on the analysis, the correct answer is:

**(d) Olfactory indicators**

### Step-by-Step Solution:

1. **Understand the question**: We need to find a term for substances that change odor in acidic or basic conditions.
- **Hint**: Look for keywords in the question that relate to odor and pH.

2. **Evaluate the options**: Go through each option and see if it fits the description.
- **Hint**: Consider what each term means and whether it relates to odor changes.

3. **Identify the correct option**: After evaluating, recognize that "olfactory indicators" specifically refers to substances that change odor based on pH.
- **Hint**: Focus on the term that directly mentions odor changes.

4. **Conclude the answer**: The correct answer is (d) Olfactory indicators.
- **Hint**: Remember that the context of the question is about odor, not just color changes.