## Core Concept
Radon exposure is a significant public health concern due to its association with lung cancer. Radon is a naturally occurring radioactive gas that can accumulate in buildings, particularly in basements and crawl spaces. It is a product of the uranium decay series and can be inhaled, leading to irradiation of the lung tissue.

## Why the Correct Answer is Right
The correct answer, **Lung Cancer**, is right because prolonged exposure to radon gas increases the risk of developing lung cancer. When radon is inhaled, its decay products can become trapped in the lungs, emitting alpha particles that damage lung tissue and DNA, leading to cancerous changes. The risk of lung cancer from radon exposure is well-documented and is considered a significant cause of lung cancer in non-smokers.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because while radiation exposure can cause various health effects, the specific and most well-known risk associated with radon exposure is lung cancer, not leukemia or other cancers directly.
- **Option B:** This option is incorrect as there is no direct, well-established link between radon exposure and the development of breast cancer.
- **Option C:** This option is incorrect because radon exposure is not commonly associated with causing gastrointestinal cancer.

## Clinical Pearl / High-Yield Fact
A critical point to remember is that radon exposure risk can be mitigated. Testing homes for radon levels and implementing measures to reduce exposure, such as improving ventilation or using radon-resistant construction materials, can significantly decrease the risk of lung cancer. Public health campaigns often focus on radon testing in homes, especially in areas known to have high radon levels.

## Correct Answer Line
**Correct Answer: D. Lung Cancer**