Wikipedia is the answer. Jimmy Wales and Larry Sanger started it in January 2001, building it as a free encyclopedia that anyone could edit collaboratively. The project had a predecessor called Nupedia, which relied on a slow expert review process, and switching to wiki based editing is what let volunteers contribute quickly and helped the site scale into the enormous encyclopedia it is now.
Wales was the businessman who funded and pushed the project forward, and Sanger, coming from a philosophy background, shaped much of the early editorial structure and is generally credited with coming up with the name itself, a blend of wiki and encyclopedia.
Looking at the other choices helps confirm this: Facebook came from Mark Zuckerberg and his Harvard classmates, Orkut was the work of Google engineer Orkut Buyukkokten and was widely used in India and Brazil for a period, and Google was started by Larry Page and Sergey Brin. Since none of these were founded by Wales and Sanger, Wikipedia remains the only correct match.