Phenolphalein does not act as an indicator for the titration between

Options

A. `HCI` and `NH_(4)OH`
B. `Ca(OH)_(2)` and `HCI`
C. `NaOH` and `H_(2)SO_(4)`
D. `KOH` and `CH_(3)COOH`

Explanation

To determine for which titration phenolphthalein does not act as an indicator, we need to understand the pH range in which phenolphthalein is effective. Phenolphthalein is an acid-base indicator that changes color in the pH range of approximately 8.3 to 10. This means it is suitable for titrations where the equivalence point falls within this pH range.

### Step-by-Step Solution:

1. **Identify the pH range of phenolphthalein**:
- Phenolphthalein changes color in the pH range of 8.3 to 10. It is colorless in acidic solutions and turns pink in basic solutions.

2. **Evaluate the titration options**:
- We need to analyze each option to see if the equivalence point falls within the pH range of phenolphthalein.

3. **Option A: HCl (strong acid) and NH4OH (weak base)**:
- The equivalence point of this titration will be acidic (pH < 7) because HCl is a strong acid and NH4OH is a weak base. Since the equivalence point is below the pH range of phenolphthalein, it cannot be used as an indicator here.

4. **Option B: Ca(OH)2 (strong base) and HCl (strong acid)**:
- The equivalence point of this titration will be neutral (pH = 7) because both reactants are strong acid and strong base. Since pH 7 is within the range of phenolphthalein, it can be used as an indicator here.

5. **Option C: NaOH (strong base) and H2SO4 (strong acid)**:
- The equivalence point of this titration will also be neutral (pH = 7). Since pH 7 is within the range of phenolphthalein, it can be used as an indicator here.

6. **Option D: KOH (strong base) and acetic acid (weak acid)**:
- The equivalence point of this titration will be basic (pH > 7) because acetic acid is a weak acid. Since the equivalence point is above pH 8.3, phenolphthalein can be used as an indicator here.

### Conclusion:
Based on the analysis, phenolphthalein does not act as an indicator for the titration between **HCl (strong acid) and NH4OH (weak base)**. Therefore, the correct answer is **Option A**.