Final answer:
Radon-222 is a hazardous radioisotope that can accumulate in homes built with materials containing uranium-238, posing a health risk due to its cancer-causing properties.
Step-by-step explanation:
The radioisotope that could be a problem in homes built from cinder blocks made from uranium mine tailings is radon-222 (Rn-222). When uranium-238 (U-238) in building materials decays, it eventually leads to the formation of radon-222, a colorless and odorless gas. Radon-222 seeps into houses through cracks in foundations and basements and accumulates in enclosed areas such as basements, especially when ventilation is poor. This accumulation poses a significant health risk as radon is a known carcinogen, potentially increasing the risk of lung cancer, particularly for individuals who smoke. To manage this risk, many countries regulate allowable radon concentrations in indoor air and require measurement of radon levels, especially when selling a house.