How many alkenes have the molecular formula C₅H₁₀ including stereoisomers

The text (chemical structures) in the image corresponds to different alkenes. Written in condensed form:

1. CH₂=CH–CH₂–CH₂–CH₃

2. CH₂=CH–CH₂–CH₂–CH₂–CH₃

3. CH₂=CH–CH₂–CH₂–CH₂–CH₃ (different structure representation)

4. CH₂=C(CH₃)–CH₃

5. CH₃–C=CH₂ (with substituents)

6. CH₂=C–CH₃ (isomeric forms)

These are different structural isomers of hexenes and pentenes.