A white ppt , is obtainned when

Options

A. A solution of `BaCl_(2)` is treated with `Na_(2)CO_(3)`
B. A solution of `CaCl_(2)` is treated with `Na_(2)SO_(3)`
C. A solution of `ZnSO_(4)` is treated with `Na_(2)S`
D. A solution of `Pb(NO_(3))_(2)`is treated with `Na_(2)CrO_(4)`

Answer

To solve the question "A white ppt is obtained when?", we will analyze the reactions mentioned in the video transcript step by step.

### Step-by-Step Solution:

1. **Reaction of BaCl2 with Na2CO3:**
- When barium chloride (BaCl2) is treated with sodium carbonate (Na2CO3), a white precipitate of barium carbonate (BaCO3) is formed.
- **Chemical Equation:**
\[ \text{BaCl}_2 + \text{Na}_2\text{CO}_3 \rightarrow \text{BaCO}_3 \downarrow + 2\text{NaCl} \]
- **Observation:** White precipitate of BaCO3.

2. **Reaction of CaCl2 with Na2SO3:**
- When calcium chloride (CaCl2) is treated with sodium sulfite (Na2SO3), a white precipitate of calcium sulfite (CaSO3) is formed.
- **Chemical Equation:**
\[ \text{CaCl}_2 + \text{Na}_2\text{SO}_3 \rightarrow \text{CaSO}_3 \downarrow + 2\text{NaCl} \]
- **Observation:** White precipitate of CaSO3.

3. **Reaction of ZnSO4 with Na2S:**
- When zinc sulfate (ZnSO4) is treated with sodium sulfide (Na2S), a white precipitate of zinc sulfide (ZnS) is formed.
- **Chemical Equation:**
\[ \text{ZnSO}_4 + \text{Na}_2\text{S} \rightarrow \text{ZnS} \downarrow + \text{Na}_2\text{SO}_4 \]
- **Observation:** White precipitate of ZnS.

4. **Reaction of Pb(NO3)2 with Na2CrO4:**
- When lead(II) nitrate (Pb(NO3)2) is treated with sodium chromate (Na2CrO4), a colored precipitate of lead chromate (PbCrO4) is formed, which is orange in color, not white.
- **Chemical Equation:**
\[ \text{Pb(NO}_3\text{)}_2 + \text{Na}_2\text{CrO}_4 \rightarrow \text{PbCrO}_4 \downarrow + 2\text{NaNO}_3 \]
- **Observation:** Orange precipitate of PbCrO4.

### Conclusion:
From the reactions analyzed, the white precipitates are formed in the first three reactions:
- BaCO3 from BaCl2 and Na2CO3
- CaSO3 from CaCl2 and Na2SO3
- ZnS from ZnSO4 and Na2S

Thus, the answer to the question is that a white precipitate is obtained in the reactions involving BaCl2 with Na2CO3, CaCl2 with Na2SO3, and ZnSO4 with Na2S.

### Final Answer:
A white precipitate is obtained in the reactions involving:
- 1. BaCl2 + Na2CO3 → BaCO3 (white ppt)
- 2. CaCl2 + Na2SO3 → CaSO3 (white ppt)
- 3. ZnSO4 + Na2S → ZnS (white ppt)