Dioxis was a potent toxic gas used by the Neimoidians of the Trade Federation at the time of and following the Battle of Naboo. The green-white gas was deadly to most carbon-based lifeforms.
Dioxis fills The Box during the Tournament on Serenno
Around 21 BBY, dioxis was used as part of a contest arranged by CountDooku on his homeworld of Serenno. Within a construct known as The Box,eleven bounty hunters competed in a series of tasks to prove their worthiness to be part of a team that would abduct Supreme ChancellorPalpatine on Naboo. The first task involved the competitors having to escape a room that was filling with dioxis gas.[1]
Thirteen years later, on Cato Neimoidia, Obi-Wan Kenobi identified a toxic gas released by Nute Gunray's mechno-chair as dioxis—though this toxin was also identified as swamp gas, the chemical weapon used by the Separatists on Ohma-D'un earlier in the Clone Wars.
Qui-Gon Jinn's line upon sensing the dioxis was simply, "Gas!" in The Phantom Menace. However, George Lucas altered this to make the gas sound more exotic and other-worldly.[source?]
The name "dioxis" is most likely derived from the real-world virulent chemical compound, dioxin.