Where is the largest reacting telescope in the world located?

The largest refracting telescope in the world is actually located at the Yerkes Observatory in Williams Bay, Wisconsin. This telescope, known as the Yerkes 40-inch telescope, was completed in 1897 and has played a significant role in astronomical research and education. It is renowned for its size and the quality of its optics, making it a historical landmark in the field of astronomy.

Other options represent notable observatories as well; for example, Mauna Kea Observatories is famous for housing several of the world's most advanced telescopes, primarily reflecting types, which are ideal for observing a wide array of astronomical phenomena. Palomar Observatory is home to the Hale Telescope, one of the largest and most significant reflecting telescopes in the world, while Mount Wilson Observatory is famous for its contributions to early 20th-century astronomy, including the discovery of the expanding universe. However, when discussing the largest refracting telescope specifically, Yerkes Observatory is the correct choice.