The following pair that cannot exist in solution is

Options

A. NaOH and KOH
B. NaCl and KCl
C. `NaHCO_3` and NaOH
D. `Na_2CO_3` and NaOH

Answer

To determine which pair cannot exist in solution, we need to analyze the nature of each pair provided in the question.

### Step-by-Step Solution:

1. **Identify the Pairs**: We need to look at the pairs mentioned in the question. The pairs are:
- Sodium Hydroxide (NaOH) and another base
- Sodium Chloride (NaCl) and Potassium Chloride (KCl)
- Sodium Bicarbonate (NaHCO₃) and Sodium Hydroxide (NaOH)
- Sodium Bicarbonate (NaHCO₃) and another salt

2. **Analyze the First Pair (NaOH and another base)**:
- Both NaOH and the other base are strong bases. When two strong bases are mixed, they do not react with each other but can coexist in solution. Therefore, they can exist together.

3. **Analyze the Second Pair (NaCl and KCl)**:
- Both NaCl and KCl are salts. They can dissolve in water without reacting with each other. Thus, they can also coexist in solution.

4. **Analyze the Third Pair (NaHCO₃ and NaOH)**:
- Sodium Bicarbonate (NaHCO₃) can act as an acid and will react with Sodium Hydroxide (NaOH), which is a strong base. The reaction will lead to neutralization, producing water and carbon dioxide. Therefore, these two cannot coexist without reacting.

5. **Analyze the Fourth Pair (NaHCO₃ and another salt)**:
- If the other salt is a neutral salt, there will be no reaction between them. Hence, they can coexist in solution.

6. **Conclusion**: The pair that cannot exist together in solution is Sodium Bicarbonate (NaHCO₃) and Sodium Hydroxide (NaOH) because they react with each other.

### Final Answer:
The pair that cannot exist in solution is Sodium Bicarbonate (NaHCO₃) and Sodium Hydroxide (NaOH).

---