Number of acyclic structural isomers of pentene are:

Answer

To determine the number of acyclic structural isomers of pentene (C5H10), we will systematically identify all possible structures.

### Step-by-Step Solution:

1. **Identify the Molecular Formula**:
Pentene has the molecular formula C5H10, indicating it is an alkene with one carbon-carbon double bond.

2. **Determine the Position of the Double Bond**:
The double bond can be located at different positions in the carbon chain. The possible positions for the double bond in pentene are:
- Pent-1-ene
- Pent-2-ene
- Pent-3-ene

**Structures**:
- **Pent-1-ene**: CH2=CH-CH2-CH2-CH3
- **Pent-2-ene**: CH3-CH=CH-CH2-CH3
- **Pent-3-ene**: CH3-CH2-CH=CH-CH3

3. **Consider Branching**:
In addition to straight-chain isomers, we can also have branched-chain isomers. For pentene, we can create branched structures by modifying the carbon chain:
- **2-Methylbut-1-ene**: CH2=CH-CH(CH3)-CH2-CH3
- **3-Methylbut-1-ene**: CH3-CH=CH(CH3)-CH2-CH3
- **2-Methylbut-2-ene**: CH3-C(CH3)=CH-CH3

4. **Count All Unique Structures**:
Now, we will count all the unique structures we have identified:
- Pent-1-ene
- Pent-2-ene
- Pent-3-ene
- 2-Methylbut-1-ene
- 3-Methylbut-1-ene
- 2-Methylbut-2-ene

5. **Final Count**:
In total, we have identified 6 unique acyclic structural isomers of pentene.

### Conclusion:
The total number of acyclic structural isomers of pentene is **6**.