Uranium-238 decays into which substance?

Uranium-238 undergoes a series of radioactive decays as part of its decay chain, ultimately leading to the production of stable lead isotopes. The first step in this decay process is the transformation of Uranium-238 into Radium-226, which is the correct answer to the question.

This process begins with the emission of an alpha particle from Uranium-238, resulting in the creation of Radium-226. Radium-226 is itself radioactive and continues to decay further down the chain, producing other elements such as Radon-222, Lead-214, and Polonium-214 designated by subsequent decay steps. Understanding this sequence is crucial for comprehending uranium's behavior in the environment, particularly in relation to radon and other decay products that may have implications for health and safety in contexts such as radon mitigation.

The choices of Radon-222, Lead-214, and Polonium-214 represent later products in the decay sequence of Uranium-238, but they do not represent the immediate decay product of Uranium-238 itself, which is why Radium-226 stands out as the correct answer.