In the third group of qualitive analysis, the precipitating reagent is `NH_(4)CI//NH_(4)OH`. The function of `NH_(4)CI` is to

Options

A. increases the ionisation of `NH_(4)OH`.
B. Supress the ionisation of `NH_(4)OH`.
C. Convert the ions of group theird into their respective chlorides.
D. Stabilise the hydroxides of group `III` cations.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Components:**
- In the qualitative analysis, we are dealing with the third group of cations. The precipitating reagents used are ammonium chloride (NH₄Cl) and ammonium hydroxide (NH₄OH).
- NH₄OH dissociates into NH₄⁺ and OH⁻ ions when dissolved in water.

2. **Role of NH₄Cl:**
- NH₄Cl also dissociates in solution to produce NH₄⁺ and Cl⁻ ions.
- The presence of NH₄Cl increases the concentration of NH₄⁺ ions in the solution.

3. **Le Chatelier's Principle:**
- According to Le Chatelier's principle, if the concentration of a product in a reversible reaction is increased, the equilibrium will shift to the left to counteract this change.
- In this case, the increased concentration of NH₄⁺ ions will shift the equilibrium of the dissociation of NH₄OH to the left, thus suppressing its ionization.

4. **Effect on Hydroxide Ion Concentration:**
- As a result of the shift in equilibrium, the concentration of OH⁻ ions will decrease because the dissociation of NH₄OH is suppressed.
- This suppression is crucial for the precipitation of the third group cations as their hydroxides.

5. **Conclusion:**
- The primary function of NH₄Cl in this context is to create a common ion effect by increasing the concentration of NH₄⁺ ions, which in turn suppresses the ionization of NH₄OH and stabilizes the conditions necessary for the precipitation of the third group cations.

**Final Answer:**
The function of NH₄Cl is to increase the concentration of NH₄⁺ ions, thereby suppressing the ionization of NH₄OH according to Le Chatelier's principle.

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