Final answer:
The hydrocarbon in question is 3-hexene, a straight-chain alkene with the molecular formula C6H12 and a double bond between the third and fourth carbon atoms.
Step-by-step explanation:
The student's question is about identifying a straight-chain hydrocarbon with the molecular formula C6H12, featuring specific types of bonds between carbon atoms. Given that the molecule has CnH2n formula, it suggests an alkene with one or more double bonds, because alkenes have such general formulas assuming non-cyclic structures. Based on the description provided by the student, this molecule has a double bond on the third and fourth carbon atoms when counting from the left. No triple bond is indicated in the problem, and the hydrocarbon is noted as completely inert, suggesting no other functional groups are present. An example of a molecule that fits this description is 3-hexene.