In J.R.R. Tolkien’s The Hobbit, Bilbo finds the One Ring during the Gollum episode.
Bilbo discovers the Ring in a passage beneath the Misty Mountains after becoming separated from the Dwarves. He later uses its power of invisibility to escape Gollum and reach the surface. At this stage of Tolkien’s writing, the Ring functions primarily as a mysterious magical possession.
In The Lord of the Rings, Tolkien greatly expanded its significance. The Ring is the One Ring forged by Sauron to control the other Rings of Power and to preserve and concentrate his power. Bilbo’s decision to give it to Frodo begins the central chain of events in the later story.
Sting is Bilbo’s sword, while the Arkenstone is the treasured jewel of Erebor. A palantír is a seeing-stone, so none of those objects is the item Bilbo finds with Gollum.