Given the task definition and input, reply with output. In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.

One of these molecules containing two geminal acceptor groups is the product of the Knoevenagel reaction. Ethers can be formed by alkoxy-mercuration between an alcohol and one of these, or by reacting a peroxy-acid with one of these. In the process of hydrogenation, some of its bonds are broken by reacting them with protons, and Lindlar's catalyst is often used to yield the cis-variety from an alkyne. Markovnikov's rules state that when hydrogen halides are added to them, the acid hydrogen attatches to the carbon with the greatest bonded hydrogens and the halide attaches to carbon with the fewest bonded hydrogens. Ethylene is the simplest member of, for 10 points, what group of unsaturated organic compounds that have at least one carbon-carbon double bond
Science