The nerve agent used in Call of Duty: Black Ops is called Nova 6.
Nova 6 is a fictional chemical weapon central to the game’s Cold War conspiracy plot. In the campaign’s backstory, Nazi scientist Friedrich Steiner develops the weapon during World War II. Soviet officers Viktor Reznov, Dimitri Petrenko, Lev Kravchenko, and Nikita Dragovich become involved in its recovery from a secret installation on Baffin Island in 1945.
The weapon’s danger is demonstrated early in the story when Dragovich exposes Petrenko and other soldiers to the gas. The Soviets later recreate Nova 6 with assistance from British scientist Daniel Clarke, making it a key part of Dragovich’s plan to deploy sleeper agents across the United States.
Nova 6 is fictional, so it should not be confused with real nerve agents such as sarin, tabun, or VX. Those names are distractors based on genuine chemical-warfare substances, while Nova 6 belongs specifically to Black Ops’ fictional universe.