Gas giant
The smallest known extrasolar planet that is likely a "gas planet" is Kepler-138d, which has the same mass as Earth but is 60% larger and therefore has a density that indicates a thick gas envelope.
Nauru
Nauru ( or ; ), officially the Republic of Nauru () and formerly known as Pleasant Island, is an island country in Micronesia, a subregion of Oceania, in the Central Pacific. Its nearest neighbour is Banaba Island in Kiribati, to the east. It further lies northwest of Tuvalu, north of the Solomon Islands, east-northeast of Papua New Guinea, southeast of the Federated States of Micronesia and south of the Marshall Islands. With residents in a area, Nauru is the smallest state in the South Pacific, smallest republic and third-smallest state by area in the world, behind only Vatican City and Monaco.