`NH_(4)Cl` is added along with `NH_(4)OH` in group (a)_____to (b)____ concentration of (c ) ____.

Answer

To solve the question regarding the addition of `NH4Cl` along with `NH4OH`, we will break it down step by step:

### Step-by-Step Solution:

1. **Identify the Purpose of Adding NH4Cl and NH4OH**:
- Ammonium chloride (NH4Cl) is added to the solution to decrease the concentration of hydroxide ions (OH⁻) when testing for certain cations.

2. **Determine the Group for Testing**:
- NH4Cl and NH4OH are specifically used in the qualitative analysis of cations in Group 3. This is because Group 3 cations can be precipitated out selectively when the concentration of hydroxide ions is controlled.

3. **Understand the Role of NH4Cl**:
- The presence of NH4Cl decreases the ionization of NH4OH due to the common ion effect. Since NH4Cl is a strong electrolyte, it provides NH4⁺ ions, which suppresses the ionization of NH4OH (a weak electrolyte).

4. **Concentration of Hydroxide Ions**:
- By adding NH4Cl, the concentration of hydroxide ions (OH⁻) is effectively decreased, which is crucial for the selective precipitation of Group 3 cations.

5. **Fill in the Blanks**:
- Based on the above understanding, we can fill in the blanks in the question:
- (a) Group 3
- (b) to decrease
- (c) hydroxide ions

### Final Answer:
`NH4Cl` is added along with `NH4OH` in group (a) **3** to (b) **decrease** concentration of (c) **hydroxide ions**.

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