In which of the following redox reaction precipitate is not formed?

Options

A. `Cr^(3+)(aq.)+Na_(2)O_(2)("Solution")to`
B. `Fe^(3+)(aq.)+(NH_(4))_(2)S to `
C. `Mn^(2+)(aq.)+H_(2)O_(2)+NH_(3)("Solution")to`
D. `Fe^(2+)(aq.)+Na_(2)O_(2)("solution")to`

Explanation

To determine which of the given redox reactions does not form a precipitate, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Option 1: Cr³⁺ + Na₂O₂**
- When chromium ions (Cr³⁺) react with sodium peroxide (Na₂O₂), they form chromate ions (CrO₄²⁻).
- The chromate ions remain in solution and do not form a precipitate.
- **Conclusion**: No precipitate is formed in this reaction.

2. **Option 2: Fe³⁺ + (NH₄)₂S**
- When iron (III) ions (Fe³⁺) react with ammonium sulfide ((NH₄)₂S), they produce iron(II) sulfide (FeS).
- Iron(II) sulfide is a solid and precipitates out of the solution.
- **Conclusion**: A precipitate (FeS) is formed in this reaction.

3. **Option 3: Mn²⁺ + H₂O₂ + NH₃**
- In this reaction, manganese (II) ions (Mn²⁺) react with hydrogen peroxide (H₂O₂) in the presence of ammonia (NH₃) to form manganese dioxide (MnO₂).
- Manganese dioxide is a solid and precipitates out of the solution.
- **Conclusion**: A precipitate (MnO₂) is formed in this reaction.

4. **Option 4: Fe²⁺ + Na₂O₂**
- When iron (II) ions (Fe²⁺) react with sodium peroxide (Na₂O₂), they form ferrous hydroxide (Fe(OH)₂).
- Ferrous hydroxide is also a solid and precipitates out of the solution.
- **Conclusion**: A precipitate (Fe(OH)₂) is formed in this reaction.

### Final Conclusion:
After analyzing all options, the only reaction that does not produce a precipitate is **Option 1: Cr³⁺ + Na₂O₂**.