Iodine (I) gains one electron to achieve a noble gas electron configuration.

Here's why:

* Iodine's Electron Configuration: Iodine has 53 electrons, with an electron configuration of [Kr] 4d¹⁰ 5s² 5p⁵.

* Noble Gas Configuration: The nearest noble gas to iodine is Xenon (Xe), which has an electron configuration of [Kr] 4d¹⁰ 5s² 5p⁶.

* Gaining an Electron: By gaining one electron, iodine's outer shell (5p) becomes filled with 6 electrons, mirroring the electron configuration of Xenon.

This process is called gaining an electron and results in the formation of the iodide ion (I⁻).