Final answer:
The process a scientist would research to convert used motor oil into gasoline involves cracking and reforming, which consist of chemically converting heavy hydrocarbons into lighter ones to produce gasoline.
Step-by-step explanation:
A scientist researching methods to convert used motor oil into gasoline is most likely investigating the process of cracking and reforming. These processes involve the chemical conversion of heavier hydrocarbons into lighter ones, which can include converting diesel fuel into gasoline. Cracking breaks larger hydrocarbon chains into smaller ones at high temperatures, often as high as 900°C. This high-temperature reaction causes the carbon-carbon bonds to break. On the other hand, reforming involves the chemical conversion of straight-chain alkanes to either branched-chain alkanes or mixtures of aromatic hydrocarbons with the aid of metal catalysts such as platinum.
Therefore, the answer to the student's question is that a scientist would be looking into cracking and reforming processes, and none of the given options (combustion, oxidation, fermentation, or polymerization) directly correspond to the correct answer. Instead, the process achieves conversion by altering the structure of hydrocarbons present in used motor oil to create gasoline.