Which of the following is NOT a short-lived decay product of radon?

Radium-226 is correctly identified as NOT a short-lived decay product of radon. To understand this more clearly, it is essential to look at the decay chain associated with radon.

Radon-222, the most common isotope of radon, undergoes radioactive decay and produces several short-lived decay products. Polonium-218, lead-214, and bismuth-214 are all part of this decay chain and have relatively brief half-lives, making them short-lived products. For instance, Polonium-218 has a half-life of about 3 minutes, Lead-214 about 27 minutes, and Bismuth-214 about 20 minutes.

In contrast, Radium-226, the precursor to radon in the decay series, has a much longer half-life of approximately 1600 years. It decays into radon-222, which then continues to produce the short-lived decay products mentioned above. Therefore, Radium-226 is not considered a short-lived decay product of radon but rather the parent isotope from which radon originates. This distinction clarifies why Radium-226 is the correct choice in this question.