Which pair will show common ion effect ?

Options

A. `BaCI_2 +Ba(NO_3)_2`
B. `NaCI+HCI`
C. `NH_4OH+NH_4CI`
D. `NaCN +KCN`

Answer

To determine which pair will show the common ion effect, we need to identify pairs of electrolytes where one is a strong electrolyte and the other is a weak electrolyte. The common ion effect occurs when a weak electrolyte is suppressed by the presence of a common ion from a strong electrolyte.

### Step-by-Step Solution:

1. **Understand the Common Ion Effect**:
- The common ion effect occurs when a weak electrolyte is in equilibrium with a strong electrolyte that shares a common ion. This results in the suppression of the ionization of the weak electrolyte.

2. **Identify Strong and Weak Electrolytes**:
- Strong electrolytes are substances that completely dissociate into ions in solution (e.g., NaCl, HCl, BaCl₂).
- Weak electrolytes partially dissociate in solution (e.g., NH₄OH, acetic acid).

3. **Analyze the Given Pairs**:
- **Barium Chloride (BaCl₂) and Barium Nitrate (Ba(NO₃)₂)**: Both are strong electrolytes.
- **Barium Hydroxide (Ba(OH)₂) and HCl**: Both are strong electrolytes.
- **Barium Hydroxide (Ba(OH)₂) and HNO₃**: Both are strong electrolytes.
- **NaCl and HCl**: Both are strong electrolytes.
- **NaCN and KCN**: Both are strong electrolytes.
- **Ammonium Hydroxide (NH₄OH) and Ammonium Chloride (NH₄Cl)**: NH₄OH is a weak electrolyte, and NH₄Cl is a strong electrolyte.

4. **Conclusion**:
- The pair that shows the common ion effect is **Ammonium Hydroxide (NH₄OH)** and **Ammonium Chloride (NH₄Cl)**, as it consists of a weak electrolyte and a strong electrolyte.

### Final Answer:
The pair that will show the common ion effect is **Ammonium Hydroxide (NH₄OH)** and **Ammonium Chloride (NH₄Cl)**.

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