______ on reductive ozonolysis gives ethanal, methanal and carbon dioxide.

Answer

To solve the question "______ on reductive ozonolysis gives ethanal, methanal, and carbon dioxide," we need to identify the compound that, when subjected to reductive ozonolysis, produces the specified products.

### Step-by-Step Solution:

1. **Understanding Reductive Ozonolysis**:
- Reductive ozonolysis is a reaction where alkenes or alkynes react with ozone (O3) followed by a reducing agent (like zinc and water) to yield carbonyl compounds (aldehydes or ketones) and sometimes carboxylic acids.

2. **Identifying the Products**:
- The products mentioned are ethanal (acetaldehyde, CH3CHO), methanal (formaldehyde, HCHO), and carbon dioxide (CO2).

3. **Determining the Starting Compound**:
- We need to find an alkene or alkyne that, when ozonolysis occurs, will yield the above products. The presence of both ethanal and methanal suggests that the starting compound must have a structure that can break down to these aldehydes.

4. **Analyzing Possible Structures**:
- A suitable candidate for ozonolysis that can yield the specified products is buta-1,2-diene (CH2=CH-CH=CH2).

5. **Performing the Reaction**:
- When buta-1,2-diene undergoes reductive ozonolysis:
- The double bonds in buta-1,2-diene will break and form:
- CH3CHO (ethanal)
- HCHO (methanal)
- CO2 (carbon dioxide)
- The reaction can be summarized as:
- CH2=CH-CH=CH2 → CH3CHO + HCHO + CO2

6. **Conclusion**:
- Therefore, the compound that fits in the blank is buta-1,2-diene (C4H6).

### Final Answer:
**Buta-1,2-diene (CH2=CH-CH=CH2)** on reductive ozonolysis gives ethanal, methanal, and carbon dioxide.

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