Incorrect statement for the use of indicator in acid-base titration is :

Options

A. Methyl orange may be used for a weak acid vs weak bas titration.
B. Phenolphthalein may be used for a strong acid vs strong base titration.
C. Methyl orange is a suitable indicator for a strong acid vs weak base titration.
D. Phenolphthalein is a suitable indicator for a weak acid vs strong base titration.

Answer

To determine the incorrect statement regarding the use of indicators in acid-base titrations, we need to analyze the properties and suitable applications of the indicators mentioned: methyl orange and phenolphthalein.

### Step-by-Step Solution:

1. **Understanding Indicators**:
- Indicators are substances that change color at a specific pH range and are used to determine the endpoint of titrations.

2. **Methyl Orange**:
- Methyl orange is an acid-base indicator that changes color in the pH range of approximately 3.2 to 4.5.
- It is suitable for titrations involving strong acids and weak bases or strong acids and strong bases.

3. **Phenolphthalein**:
- Phenolphthalein is another acid-base indicator that changes color in the pH range of approximately 8.3 to 10.5.
- It is suitable for titrations involving strong acids and strong bases or weak acids and strong bases.

4. **Analyzing the Statements**:
- **Statement 1**: Methyl orange may be used for a weak acid or a weak base titration.
- This statement is incorrect because methyl orange is not suitable for weak acid versus weak base titrations.
- **Statement 2**: Phenolphthalein may be used for strong acid versus strong base titration.
- This statement is correct.
- **Statement 3**: Methyl orange is a suitable indicator for strong acid versus weak base titration.
- This statement is correct.
- **Statement 4**: Phenolphthalein is a suitable indicator for weak acid versus strong base titration.
- This statement is correct.

5. **Conclusion**:
- The incorrect statement is **Statement 1**: "Methyl orange may be used for a weak acid or a weak base titration."

### Final Answer:
The incorrect statement for the use of indicator in acid-base titration is: **Methyl orange may be used for a weak acid or a weak base titration.**

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