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.

[Q]: An approximation of it named for Russell uses the TDS value to determine one of its parameters via the Langelier approximation, while one constant that appears in it has units of moles per kilogram to the one half power, according the Bates-Guggenheim convention. Along with Guggenheim, Scatchard and Bronsted improved upon this model by developing the SIT theory, and that model has a better fit than a modification of it named for Davies. This relationship assumes the existence of only long-range interactions, and it was extended to account for Brownian motion by Lars Onsager. It assumes that the solvent is structure-less and that the solution is dilute, and the theory behind it implies that the electrostatic potential falls off exponentially when r is greater than the atomic radius due to screening by counter ions. For 10 points, identify this equation which is used to calculate the activity coefficients, and is named for a German and a Dutch scientist.
[A]: Science

[Q]: Koussevitsky commissioned this man to write his Symphony for Organ and Orchestra. He wrote an opera that opens with the arrival of Laurie Moss' graduation gown. Three ascending notes in the brass open a work by this man that debuted at tax time. He quoted folk songs like "Camptown Races" in a work that incorporates spoken-word readings of texts like the Gettysburg Address. He used themes from the Shaker hymn "Simple Gifts" for ballet choreographed by Martha Graham. Another of his ballets contains a "Hoe Down. " He composed Fanfare for the Common Man and the ballets Rodeo and Billy the Kid. For 10 points, name this composer of Appalachian Spring.
[A]: Fine Arts

[Q]: A scene in this work at the Gate of Wisdom sees a priest convince the protagonist that women have trivial opinions. In one of its scenes, a character falsely claims that he rescued the protagonist from a snake, after which three women hand the liar a rock and padlock his mouth shut. This opera features the famous Tremble not, my dear son aria, and its incredibly demanding aria Der Hoelle Rache requires a range up to F6 for its soprano role. A man dressed in birds feathers in this opera is Papageno, who is a servant of the villain. The plot of this opera centers on the love of Tamino for the maid Pamina, and the attempts to thwart the relationship by the Queen of the Night. For 10 points, name this work that features an instrument which can change mens hearts, an opera by Wolfgang Amadeus Mozart.
[A]:
Fine Arts