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.

This functional group can react with double bonds via the (2+4) Huisgen cycloaddition reaction to form a five-membered ring similar to pyrrole. It can react with tertiary alcohols and alkenes to generate imines, and it can bond to substituted phosphines via Staudinger ligation. Esters reacted with hydrazine followed by nitrous acid can produce this group attached to a carbonyl carbon, from where it can produce water and an isocyanate in the Curtius rearrangement. It also displaces halides in alkyl halides, which can be reduced by lithium aluminum hydride to primary amines. These reactions are driven by the production of nitrogen gas, which this molecule can quickly do if heated. For that reason its sodium salt is used in airbags. FTP, name this trinitrogen anion.
Science