Which of the following combination of reagent(s) produce observable change in aqueous medium?

Options

A. `Ba(OH)_(2)` solution+`SO_(2)(g)`
B. `AgF` solution+`NaNO_(3)` solution
C. `Pb(OA c)_(2)` soution+`Na_(2)CO_(3)` solution
D. `CuCl_(2)` solution`+NH_(3)` (excess)

Explanation

To determine which combinations of reagents produce observable changes in an aqueous medium, we will analyze each option provided in the question step by step.

### Step 1: Analyze Option 1
**Reagents:** Ba(OH)₂ (aqueous) + SO₂ (gaseous)

- When barium hydroxide reacts with sulfur dioxide, it produces barium sulfite (BaSO₃), which is a precipitate.
- **Observable Change:** The formation of a solid precipitate indicates a visible change.

### Step 2: Analyze Option 2
**Reagents:** AgF (aqueous) + NaNO₃ (aqueous)

- In this case, both silver fluoride and sodium nitrate are soluble in water, and there is no reaction between them.
- **Observable Change:** No observable change occurs as no precipitate or gas is formed.

### Step 3: Analyze Option 3
**Reagents:** Pb(OAc)₂ (aqueous) + Na₂CO₃ (aqueous)

- Lead(II) acetate reacts with sodium carbonate to form lead(II) carbonate (PbCO₃), which is an insoluble precipitate, and sodium acetate (CH₃COONa).
- **Observable Change:** The formation of a solid precipitate indicates a visible change.

### Step 4: Analyze Option 4
**Reagents:** CuCl₂ (aqueous) + NH₃ (excess)

- When copper(II) chloride reacts with excess ammonia, it forms a deep blue complex known as tetraamminecopper(II) chloride (Cu(NH₃)₄Cl₂).
- **Observable Change:** The change in color to deep blue indicates a visible change.

### Conclusion
Based on the analysis:
- **Option 1:** Observable change (precipitate)
- **Option 2:** No observable change (no reaction)
- **Option 3:** Observable change (precipitate)
- **Option 4:** Observable change (color change)

Thus, the combinations of reagents that produce observable changes in aqueous medium are **Option 1, Option 3, and Option 4**. **Option 2** does not produce any observable change.

### Final Answer
The correct options that produce observable changes in aqueous medium are **Option 1, Option 3, and Option 4**.

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