Which of the following represents the second alkene in the series?

The second alkene in the series of alkenes is propene. Alkenes are a group of hydrocarbons with at least one carbon-carbon double bond, and they follow a specific naming convention based on the number of carbon atoms.

To understand this, consider the structure of the alkenes:

• Ethene has 2 carbon atoms (C2H4).

• Propene, which comes next, has 3 carbon atoms (C3H6).
• Butene has 4 carbon atoms (C4H8).
• Hexene has 6 carbon atoms (C6H10).

Thus, propene is clearly the second alkene as it has three carbon atoms, fitting the sequence where each subsequent alkene has one additional carbon atom more than the last. The term "second alkene" specifically refers to the one that follows ethene (the first alkene) in terms of molecular structure, confirming that propene is indeed the correct representation for this choice.