HAZMAT Technician Practice Exam

Which type of unsaturated hydrocarbon has at least one double bond?

1. Alkanes

2. Alkenes

3. Alkynes

4. Saturated hydrocarbons

The correct answer is: Alkenes

The identification of alkenes as the correct type of unsaturated hydrocarbon with at least one double bond is rooted in the fundamental characteristics of hydrocarbons. Alkenes are defined specifically by the presence of one or more double bonds between carbon atoms in their molecular structure, distinguishing them from other categories of hydrocarbons. Alkanes, on the other hand, consist solely of single bonds between carbon atoms, making them saturated hydrocarbons. They do not possess any double or triple bonds, which is a key feature of unsaturations. Alkynes, while also unsaturated hydrocarbons, are characterized by having at least one triple bond, rather than a double bond. This further clarifies that while they are unsaturated, they fall into a different category due to the nature of their bonding. Saturated hydrocarbons, by definition, do not contain double or triple bonds, aligning them with alkanes. They are fully "saturated" with hydrogen atoms, meaning each carbon atom is bonded to the maximum number of hydrogen atoms possible. Thus, the specific nature of alkenes, marked by the presence of double bonds, makes them the unique classification in the question that meets the criteria established for unsaturated hydrocarbons.