Final answer:
Alkenes and cyclic hydrocarbons differ from hydrocarbons without double bonds or ring structures. Longer hydrocarbons have more carbon atoms, while branched hydrocarbons have additional chains branching off. Identical hydrocarbons have the same formula and structure.
Step-by-step explanation:
Hydrocarbons with a double bond are called alkenes and those with a ring structure are called cyclic hydrocarbons. The presence of a double bond or a ring structure leads to different physical and chemical properties compared to hydrocarbons without these features. A hydrocarbon that is longer refers to one that has a greater number of carbon atoms in its chain, while a branched hydrocarbon has additional carbon chains branching off from the main chain. Identical hydrocarbons have the same molecular formula and structure.