An unknown mixture contains one or two of the following: `CaCO_(3),BaCl_(2),AgNO_(3),Na_(2)SO_(4),ZnSO_(4) and NaOH`. The mixture is completely soluble in water and solution gives pink colour with phenolphthalein. When dilute hydrochloric acid is gradually added to the solution, a precipitate is formed which dissolved with further addition of the acid.
Q. Which of the following combination of compounds is soluble in water?

Options

A. `BaCl_(2) and AgNO_(3)`
B. `AgNO_(3) and NaOH`
C. `BaCl_(2) and Na_(2)SO_(4)`
D. `ZnSO_(4) and` excess `NaOH`

Explanation

To solve the problem, we need to analyze the given compounds and their solubility in water, as well as their behavior when hydrochloric acid (HCl) is added.

### Step-by-Step Solution:

1. **Identify the Compounds**: The unknown mixture contains one or two of the following compounds:
- CaCO₃ (Calcium Carbonate)
- BaCl₂ (Barium Chloride)
- AgNO₃ (Silver Nitrate)
- Na₂SO₄ (Sodium Sulfate)
- ZnSO₄ (Zinc Sulfate)
- NaOH (Sodium Hydroxide)

2. **Solubility in Water**:
- CaCO₃: Insoluble in water
- BaCl₂: Soluble in water
- AgNO₃: Soluble in water
- Na₂SO₄: Soluble in water
- ZnSO₄: Soluble in water
- NaOH: Soluble in water

From this, we can see that BaCl₂, AgNO₃, Na₂SO₄, ZnSO₄, and NaOH are soluble in water.

3. **Phenolphthalein Test**: The solution gives a pink color with phenolphthalein, indicating that the solution is basic. This suggests the presence of NaOH or a basic compound.

4. **Addition of Dilute HCl**: When dilute HCl is added, a precipitate forms, which dissolves with further addition of the acid. This indicates that the precipitate is likely a hydroxide that is soluble in excess acid.

5. **Analyzing Possible Combinations**:
- **Option 1: BaCl₂ + AgNO₃**: Both are soluble, but they do not produce a precipitate with HCl.
- **Option 2: AgNO₃ + NaOH**: AgNO₃ is soluble, but NaOH would give a basic solution without a precipitate that dissolves in HCl.
- **Option 3: BaCl₂ + Na₂SO₄**: Both are soluble, but do not react to form a precipitate with HCl.
- **Option 4: ZnSO₄ + Excess NaOH**: ZnSO₄ is soluble, and when NaOH is added, it forms sodium zincate (Na₂ZnO₂), which is also soluble. Upon adding HCl, zinc hydroxide (Zn(OH)₂) precipitates, which dissolves in excess HCl to form zinc chloride (ZnCl₂), confirming the behavior described.

6. **Conclusion**: The only combination of compounds that is soluble in water and fits all the criteria given in the problem is **ZnSO₄ and excess NaOH**.

### Final Answer:
The combination of compounds that is soluble in water is **ZnSO₄ and excess NaOH** (Option 4).

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