Which celestial body is classified as a dwarf planet?

Eris is classified as a dwarf planet because it meets the criteria established by the International Astronomical Union (IAU). To be classified as a dwarf planet, a celestial body must orbit the Sun, have sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a nearly round shape (hydrostatic equilibrium), and not have cleared its neighboring region of other objects. Eris is similar in size to Pluto and was one of the key discoveries that led to the redefinition of what constitutes a planet.

The other options are not classified as dwarf planets. The Moon is a natural satellite, Jupiter is a gas giant, and Mercury is a terrestrial planet. None of these options fulfill the specific requirements outlined for dwarf planets, which is why Eris is the only appropriate choice in this context.