`BiCl_(3)` can be reduced to metallic bismuth by:

Options

A. `H_(2)S`
B. `SO_(2)`
C. `FeSO_(4)`
D. `Na_(2)[Sn(OH)_(4)]`

Answer

To reduce bismuth chloride (BiCl₃) to metallic bismuth (Bi), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reactants**: We start with bismuth chloride (BiCl₃) as our reactant. We need a reducing agent to convert it to metallic bismuth.

2. **Choose the Reducing Agent**: Among the given options, we need to determine which one can effectively reduce BiCl₃ to Bi. The options provided are:
- H₂S (hydrogen sulfide)
- SO₂ (sulfur dioxide)
- Ferrous sulfate (FeSO₄)
- Na₂Sn(OH)₄ (sodium stannate)

3. **Evaluate the Reducing Agents**:
- H₂S is a mild reducing agent and may not be strong enough to reduce BiCl₃ to Bi.
- SO₂ is also a weak reducing agent and typically oxidizes rather than reduces.
- Ferrous sulfate (FeSO₄) can act as a reducing agent, but it is not the most effective for this reaction.
- Na₂Sn(OH)₄ is a strong reducing agent and is commonly used for the reduction of metal halides to their respective metals.

4. **Write the Reaction**: The reaction of BiCl₃ with Na₂Sn(OH)₄ in a basic medium (using sodium hydroxide, NaOH) can be represented as follows:
\[ \text{BiCl}_3 + \text{Na}_2\text{Sn(OH)}_4 \rightarrow \text{Bi} + \text{Na}_2\text{SnO}_6 + \text{NaCl} \]

5. **Balance the Reaction**: To balance the reaction, we ensure that the number of atoms for each element is equal on both sides. The balanced equation can be represented as:
\[ 2 \text{BiCl}_3 + 3 \text{Na}_2\text{Sn(OH)}_4 \rightarrow 2 \text{Bi} + 3 \text{Na}_2\text{SnO}_6 + 6 \text{NaCl} \]

6. **Conclusion**: From the analysis, we conclude that bismuth chloride (BiCl₃) can be effectively reduced to metallic bismuth (Bi) using sodium stannate (Na₂Sn(OH)₄). Therefore, the correct answer is option 4: Na₂Sn(OH)₄.