`NH_(4)CI` can be replaced by `(NH_(4))_(2)SO_(4)` in group III.

Explanation

To determine whether \( NH_4Cl \) can be replaced by \( (NH_4)_2SO_4 \) in group III cation analysis, we will analyze the role of each compound and the implications of their use in the qualitative analysis of cations.

### Step-by-Step Solution:

1. **Identify Group III Cations**:
- The group III cations include \( Fe^{3+}, Al^{3+}, Zn^{2+}, \) and \( Ni^{2+} \). These cations are typically precipitated using ammonium hydroxide (\( NH_4OH \)) in the presence of a strong salt.

2. **Role of \( NH_4Cl \)**:
- \( NH_4Cl \) is a strong electrolyte that provides \( NH_4^+ \) ions. When added to the solution, it suppresses the dissociation of \( NH_4OH \) due to the common ion effect. This is crucial for maintaining the pH required for the precipitation of group III cations.

3. **Common Ion Effect**:
- The common ion effect states that the addition of an ion common to a solution will suppress the dissociation of a weak electrolyte. In this case, \( NH_4^+ \) from \( NH_4Cl \) helps maintain the equilibrium necessary for the selective precipitation of group III cations.

4. **Consider \( (NH_4)_2SO_4 \)**:
- \( (NH_4)_2SO_4 \) also provides \( NH_4^+ \) ions and is a strong electrolyte. However, it also introduces sulfate ions (\( SO_4^{2-} \)) into the solution.

5. **Potential Issues with Sulfate Ions**:
- The presence of sulfate ions can lead to the formation of precipitates with other cations in the solution. For example, barium sulfate (\( BaSO_4 \)), calcium sulfate (\( CaSO_4 \)), and magnesium sulfate (\( MgSO_4 \)) are insoluble and can precipitate out, interfering with the analysis of group III cations.

6. **Conclusion**:
- Due to the potential for unwanted precipitates from sulfate ions, \( (NH_4)_2SO_4 \) cannot effectively replace \( NH_4Cl \) in the analysis of group III cations. Therefore, the statement is **false**.

### Final Answer:
**False** - \( NH_4Cl \) cannot be replaced by \( (NH_4)_2SO_4 \) in group III cation analysis.