Which of the following is a geological source of radon?

Granite is indeed a significant geological source of radon. It is an igneous rock that contains a higher concentration of uranium and other radioactive elements within its mineral composition compared to other types of rock. When uranium decays, it produces radon gas as a byproduct. This process occurs naturally over time, leading to the release of radon into the surrounding environment.

Granite is commonly found in many regions and can influence the levels of radon in homes, especially when those structures are built on or near granite formations. Understanding the geological composition of an area, especially the presence of granite, is crucial for assessing radon exposure risks, as homes built on or near such geological sources may have elevated radon levels requiring monitoring and mitigation.

The other materials listed, such as sandstone, clay, and basalt, may contain radon but are generally not recognized as significant sources compared to granite, primarily due to their lower uranium content or differing geological characteristics.