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.

The acceleration of some Claisen rearrangements in emulsions of this substance was studied by Karl Barry Sharpless. The second stage of the Ostwald process is carried out with an absorption apparatus containing this byproduct. It can be removed from mixtures with magnesium or sodium sulfate, and alkali metals are extremely reactive with it. This compound, frequently used as a moderator for nuclear reactors, can contain a deuterium atom in its "heavy" variety. Along with carbon dioxide, it is produced in combustion reactions, and its triple point is used to define the Kelvin. For 10 points, name this compound with bent molecular geometry and formula H2O.
Science