Task: Text Categorization
Input (English): compound can be used in rocket propellants, and corrosion of metal by it can be inhibited by phosphorous pentafluoride or a small amount of hydrogen fluoride. Another early process to produce this compound involved blowing air through an arc furnace at temperatures greater than 3000 C, cooling the products, and bringing them into contact with water, and was developed by Birkeland and Eyde. It is commonly added to solutions to remove unwanted ions which react with silver nitrate in a test for halide ions. It has two "fuming" forms; it appears white when highly concentrated, and red when an additional precursor is added to the solution. For 10 points, name this strong acid which is formed in the Ostwald Process and can be used with sulfuric acid to add an NO2 group to an aromatic ring.
Output (English): Science