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.

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. 
Science

A scordatura g-sharp-D-A-E-flat violin section characterizes one of this man's works, which features the movements "Relaxation" and "Recruiting Dance. " One of this man's works has the violinist play on the G and D strings to imitate the voice of a bear and opens with the movement "Bagpipers. " Besides Contrasts and Sonatina on Themes from Transylvania, he produced songs like "Red Apple" following an influential performance by Lidi Dosa. His early performances of Strauss' Ein Heldenleben inspired the patriotic symphonic poem, Kossuth, while with Zoltan Kodaly he put out an "appeal" to his people, resulting in collections like For Children. Also known for ballets like The Wooden Prince and The Miraculous Mandarin, for 10 points, name this composer who collected many folk songs from his native Hungary, also known for the opera, Duke Bluebeard's Castle.
Fine Arts

This ruler dispatched the Nestorian monk, Rabban Sauma, as a diplomat to Christian Europe. With the help of his general, Hundred Eyes Bayan, he successfully besieged the cities of Xianyang and Fencheng. After those victories, he conquered the Southern Song and declared himself ruler of the Yuan Dynasty. This man sent an expedition to Kyushu, which was defended by a stone wall along Hakkata Bay; however, that expedition failed when a typhoon called the kamikaze destroyed this ruler's navy. For 10 points, name this Mongol ruler visited by Marco Polo who was the grandson of Genghis.

History