Which radioactive gas is a decay product of radium?

The radioactive gas that is a decay product of radium is radon. Specifically, radium-226 undergoes alpha decay to form radon-222, a colorless, odorless noble gas.

Radon is part of the uranium-238 decay series. Uranium decays through several intermediate elements, including thorium and radium, before producing radon. Radon-222 has a half-life of about 3.82 days, after which it alpha-decays into polonium-218. Its later decay products eventually lead to stable lead-206.

The gas’s mobility makes it different from most radioactive elements in the chain. Radon can escape from soil, rocks, groundwater, and uranium-bearing materials, then accumulate in poorly ventilated buildings. Its short-lived decay products can attach to airborne particles and are a significant cause of lung-cancer risk after long-term exposure.

Argon and neon are also noble gases, but they are not the characteristic decay product of radium. Helium can be produced during alpha decay, but it is the alpha particle’s eventual captured form, not the named gaseous daughter of radium-226.