In how many of the following reactions one of the products is obtained as a black precipitate ?
(i)`Bi(OH)_3 darr +[Sn(OH)_4]^(2-)(aq)to`Products
(ii)`Bi^(3+)(aq)+I^(-)(aq)("not in excess")to`Products
(iii)`Bi^(3+)(aq)+H_2S(g)overset(H^+)to`Products
(iv)`[Bil_4]^(-)(aq)+H_2O(l)overset("dilution")to`Products
(v)`Bi^(3+)(aq)+C_9H_7ON(5%)+H^(+)(aq)+I^(-)(6M)to` Products
(vi)`Bi^(3+)(aq)+C_6H_3(OH)_3(10%)to`Products
(vii)`BiO. OH darr + H_2O_2(aq)to` Products

Explanation

To determine how many of the given reactions produce a black precipitate, we will analyze each reaction step by step.

### Step 1: Analyze the Reactions

1. **Reaction (i)**:
\[ \text{Bi(OH)}_3 + \text{[Sn(OH)}_4]^{2-} \rightarrow \text{Products} \]
- The products are Bi and Sn(OH)6^{2-}.
- **Black Precipitate**: Yes, Bi is a black precipitate.

2. **Reaction (ii)**:
\[ \text{Bi}^{3+} + \text{I}^- \rightarrow \text{Products} \]
- The product is BiI3.
- **Black Precipitate**: Yes, BiI3 is a black precipitate.

3. **Reaction (iii)**:
\[ \text{Bi}^{3+} + \text{H}_2\text{S} \rightarrow \text{Products} \]
- The product is Bi2S3.
- **Black Precipitate**: Yes, Bi2S3 is a black precipitate.

4. **Reaction (iv)**:
\[ \text{[BiI}_4]^{-} + \text{H}_2\text{O} \rightarrow \text{Products} \]
- The product is Bi3 and I^-.
- **Black Precipitate**: Yes, Bi3 is a black precipitate.

5. **Reaction (v)**:
\[ \text{Bi}^{3+} + \text{C}_9\text{H}_7\text{ON} + \text{H}^+ + \text{I}^- \rightarrow \text{Products} \]
- The product is a complex, C9H7ON·HBi4.
- **Black Precipitate**: No, this is a red precipitate.

6. **Reaction (vi)**:
\[ \text{Bi}^{3+} + \text{C}_6\text{H}_3(\text{OH})_3 \rightarrow \text{Products} \]
- The product is Bi(C6H3O3)3.
- **Black Precipitate**: No, this is a yellow precipitate.

7. **Reaction (vii)**:
\[ \text{BiO.OH} + \text{H}_2\text{O}_2 \rightarrow \text{Products} \]
- The product is BiO3^{-}.
- **Black Precipitate**: No, this is a yellowish-brown precipitate.

### Step 2: Count the Reactions Producing Black Precipitates

From the analysis:
- Reactions (i), (ii), (iii), and (iv) produce black precipitates.
- Reactions (v), (vi), and (vii) do not produce black precipitates.

### Conclusion

**Total Reactions Producing Black Precipitate**: 4