Which of the following combinations in an aqueous medium will give a yellow ppt. ?

Options

A. `AgNO_(3) + NaBr`
B. `Pb(CH_(3)COO)_(2) + Na_(2)CrO_(4)`
C. `Fe^(3+) + overset(Θ)SCN`
D. None of these

Answer

To determine which combinations in an aqueous medium will give a yellow precipitate, we will analyze each option provided:

### Step-by-Step Solution:

1. **Analyze the first combination: AgNO3 + NaBr**
- When silver nitrate (AgNO3) reacts with sodium bromide (NaBr), it forms silver bromide (AgBr) as a precipitate.
- The reaction is:
\[ \text{AgNO}_3 + \text{NaBr} \rightarrow \text{AgBr (s)} + \text{NaNO}_3 \]
- **Observation**: AgBr is known to be a yellow precipitate.

2. **Analyze the second combination: Pb(CH3COO)2 + Na2CrO4**
- When lead acetate (Pb(CH3COO)2) reacts with sodium chromate (Na2CrO4), it forms lead chromate (PbCrO4) as a yellow precipitate.
- The reaction is:
\[ \text{Pb(CH}_3\text{COO)}_2 + \text{Na}_2\text{CrO}_4 \rightarrow \text{PbCrO}_4 (s) + 2 \text{NaCH}_3\text{COO} \]
- **Observation**: PbCrO4 is a well-known yellow precipitate.

3. **Analyze the third combination: Fe3+ + KCN**
- When iron (III) ions (Fe3+) react with potassium cyanide (KCN), they form a complex ion, specifically ferric cyanide, which does not produce a yellow precipitate.
- The reaction is:
\[ \text{Fe}^{3+} + 6 \text{KCN} \rightarrow \text{[Fe(CN)}_6]^{3-} + 6 \text{K}^+ \]
- **Observation**: The resulting complex is typically red in color, not yellow.

4. **Conclusion**:
- From the analysis, the first combination (AgNO3 + NaBr) and the second combination (Pb(CH3COO)2 + Na2CrO4) both yield yellow precipitates.
- The third combination does not yield a yellow precipitate.

### Final Answer:
The combinations that will give a yellow precipitate are:
- **Option A: AgNO3 + NaBr**
- **Option B: Pb(CH3COO)2 + Na2CrO4**