The pair of compound which cannot exist in solution is:

Options

A. `NaHCO_(3) and NaOH`
B. `Na_(2)SO_(3) and NaHCO_(3)`
C. ` Na_(2)CO_(3) and NaOH`
D. `NaHCO_(3) and NaCl`

Answer

To solve the question about which pair of compounds cannot exist in solution, we need to analyze the given options based on their chemical properties and potential reactions.

### Step-by-Step Solution

1. **Understanding the Compounds**:
- We have four pairs of compounds to analyze:
- (A) Sodium bicarbonate (NaHCO3) and Sodium hydroxide (NaOH)
- (B) Sodium sulphite (Na2SO3) and Sodium carbonate (Na2CO3)
- (C) Sodium carbonate (Na2CO3) and Sodium hydroxide (NaOH)
- (D) Sodium carbonate (Na2CO3) and Sodium chloride (NaCl)

2. **Analyzing Option A (NaHCO3 and NaOH)**:
- Sodium bicarbonate (NaHCO3) is a salt of a weak acid (carbonic acid, H2CO3) and a strong base (NaOH).
- When mixed, NaHCO3 can act as an acid and react with NaOH to form sodium carbonate (Na2CO3) and water (H2O).
- Therefore, these two compounds will react and cannot coexist in solution.

3. **Analyzing Option B (Na2SO3 and Na2CO3)**:
- Sodium sulphite (Na2SO3) and sodium carbonate (Na2CO3) are both salts and do not have any strong acid-base reaction between them.
- They can exist together in solution without reacting.

4. **Analyzing Option C (Na2CO3 and NaOH)**:
- Sodium carbonate (Na2CO3) is a salt of a weak acid (carbonic acid) and a strong base.
- Sodium hydroxide (NaOH) is also a strong base.
- There is no significant reaction between Na2CO3 and NaOH, so they can coexist in solution.

5. **Analyzing Option D (Na2CO3 and NaCl)**:
- Sodium carbonate (Na2CO3) and sodium chloride (NaCl) are both salts and do not react with each other.
- They can exist together in solution without any reaction.

6. **Conclusion**:
- The only pair of compounds that cannot exist in solution because they react with each other is **Option A: Sodium bicarbonate (NaHCO3) and Sodium hydroxide (NaOH)**.

### Final Answer:
The pair of compounds that cannot exist in solution is **Option A: Sodium bicarbonate (NaHCO3) and Sodium hydroxide (NaOH)**.