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

Rosenheim and Callow developed a test in which a mixture of this compound and metal acetates are used to detect the presence of sterols. Millon's reagent is a solution of mercury in this substance and a similar substance, which turns red in the presence of phenolic compounds and is useful in detecting tyrosine residues. The commercial production of this compound begins with the combustion of ammonia using a platinum-rhodium catalyst; that process is the Ostwald process. For 10 points, identify this acid which is found with hydrochloric acid in aqua regia, and has chemical formula HNO3.
Science

A ship flying dozens of national flags and a red sun blurred by a cloud appear in the background of the black-clothed, palette-holding central figure in his Myself: Portrait Landscape, while a dark-skinned man in a traditional clown costume locks arms with a woman in peasant dress in front of several bare trees in his Carnival Evening. For 10 points, name this artist who also painted a work in which multicolored stripes adorn the dress of the title figure, who is holding a walking stick near a lute and a lion, called The Sleeping Gypsy.

Fine Arts