Hydrocarbon family identification: among the following, identify the naphthene (saturated cycloparaffin) that represents a cycloalkane rather than an olefin, diene, or acetylene.

Introduction / Context:
Petroleum hydrocarbon families include paraffins (alkanes), naphthenes (cycloparaffins), aromatics, and olefins/diolefins. Recognizing structural features helps predict fuel behavior such as octane response, smoke point, and stability. This question asks you to select the naphthene—i.e., a saturated cyclic hydrocarbon.

Given Data / Assumptions:

• Naphthenes are saturated rings (cycloalkanes).
• Options include unsaturated acyclic hydrocarbons and one saturated cyclic.
• We classify by bonding and ring presence.

Concept / Approach:
Butene (C4H8) is an olefin (contains one C=C). Butadiene (C4H6) is a diene with two double bonds. Acetylene (C2H2) is an alkyne with a triple bond. Cyclohexane (C6H12) is a saturated ring and is the archetypal naphthene. Thus, only cyclohexane fits the definition of a naphthene among the choices.

Step-by-Step Solution:

Verification / Alternative check:
Hydrocarbon family tables in refining texts classify cyclohexane under naphthenes; the rest are unsaturated acyclic species.

Why Other Options Are Wrong:

Common Pitfalls:
Equating “naphthene” with “aromatic” due to similar-sounding names; aromatics contain conjugated rings with special stability, which cyclohexane lacks.

Final Answer:
Cyclohexane