In the titration of `NH_(4)OH)` with HCl, the indicator which cannot be used is :

Options

A. Phenolphthalein
B. Methyl orange
C. Methyl red
D. Both methyl orange and methyl red

Explanation

To determine the indicator that cannot be used in the titration of ammonium hydroxide (NH₄OH) with hydrochloric acid (HCl), we need to analyze the pH range at the equivalence point of the titration and the pH ranges of the indicators provided.

### Step-by-Step Solution:

1. **Identify the Nature of the Reactants**:
- HCl is a strong acid.
- NH₄OH (ammonium hydroxide) is a weak base.

2. **Understand the Reaction**:
- The reaction between HCl and NH₄OH can be represented as:
\[ \text{HCl} + \text{NH}_4\text{OH} \rightarrow \text{NH}_4\text{Cl} + \text{H}_2\text{O} \]
- This reaction produces ammonium chloride (NH₄Cl), which is a salt that will undergo hydrolysis in water.

3. **Determine the pH at the Equivalence Point**:
- Since we are titrating a strong acid with a weak base, the resulting solution at the equivalence point will be acidic.
- The pH at the equivalence point will typically be less than 7, generally falling in the range of 4 to 6.

4. **Evaluate the Indicators**:
- **Phenolphthalein**: Changes color at a pH range of 8.3 to 10. This is not suitable for our titration since the pH at the equivalence point is below 7.
- **Methyl Orange**: Changes color at a pH range of 3.1 to 4.5. This is suitable as it encompasses the pH range we expect at the equivalence point.
- **Methyl Red**: Changes color at a pH range of 4.2 to 6.2. This is also suitable for our titration.
- **Bromothymol Blue**: Changes color at a pH range of 6.0 to 7.6. This may be suitable, depending on the exact pH at the equivalence point.

5. **Conclusion**:
- The indicator that cannot be used in the titration of NH₄OH with HCl is **Phenolphthalein** because its color change occurs at a pH that is too high for the acidic endpoint of this titration.

### Final Answer:
The indicator which cannot be used is **Phenolphthalein**.