How many of the following on reductive ozonolysis will give ethanal as one of the products?
2-Methylbut-2-ene, 2-methylpropene, but-2-ene, propene, ethene, pent-2-ene, pent-3-ene, hex-3-ene

Explanation

To determine how many of the given compounds will yield ethanal (acetaldehyde) as one of the products upon reductive ozonolysis, we will analyze each compound step by step.

### Step-by-Step Solution:

1. **2-Methylbut-2-ene**:
- Structure: CH3-C(CH3)=C(CH3)-CH3
- Upon ozonolysis, the double bond breaks and forms two products:
- CH3-C(=O)-CH3 (acetone)
- CH3-CHO (ethanal)
- **Result**: Ethanal is produced.

2. **2-Methylpropene**:
- Structure: CH2=C(CH3)-CH3
- Upon ozonolysis, the double bond breaks and forms:
- HCHO (formaldehyde)
- CH3-CHO (ethanal)
- **Result**: Ethanal is produced.

3. **But-2-ene**:
- Structure: CH3-CH=CH-CH3
- Upon ozonolysis, the double bond breaks and forms:
- CH3-CHO (ethanal)
- CH3-CHO (ethanal)
- **Result**: Ethanal is produced.

4. **Propene**:
- Structure: CH2=CH-CH3
- Upon ozonolysis, the double bond breaks and forms:
- HCHO (formaldehyde)
- CH3-CHO (ethanal)
- **Result**: Ethanal is produced.

5. **Ethene**:
- Structure: CH2=CH2
- Upon ozonolysis, the double bond breaks and forms:
- HCHO (formaldehyde)
- HCHO (formaldehyde)
- **Result**: Ethanal is NOT produced.

6. **Pent-2-ene**:
- Structure: CH3-CH=CH-CH2-CH3
- Upon ozonolysis, the double bond breaks and forms:
- CH3-CHO (ethanal)
- CH3-CH2-CHO (propionaldehyde)
- **Result**: Ethanal is produced.

7. **Pent-3-ene**:
- Structure: CH3-CH2-CH=CH-CH3
- Upon ozonolysis, the double bond breaks and forms:
- CH3-CH2-CHO (propionaldehyde)
- CH3-CHO (ethanal)
- **Result**: Ethanal is produced.

8. **Hex-3-ene**:
- Structure: CH3-CH2-CH=CH-CH2-CH3
- Upon ozonolysis, the double bond breaks and forms:
- CH3-CH2-CHO (propionaldehyde)
- CH3-CH2-CHO (propionaldehyde)
- **Result**: Ethanal is NOT produced.

### Summary of Results:
- Compounds that produce ethanal:
1. 2-Methylbut-2-ene
2. 2-Methylpropene
3. But-2-ene
4. Propene
5. Pent-2-ene
6. Pent-3-ene

- Compounds that do NOT produce ethanal:
1. Ethene
2. Hex-3-ene

### Final Count:
- Total compounds producing ethanal: **6 out of 8**.