Final answer:
To treat thyroid cancer, helium and strontium can be eliminated from the list of possible atoms; helium is not used for thyroid cancer treatment, and strontium is specific to bone cancer pain relief.
Step-by-step explanation:
When considering the list of possible atoms to treat thyroid cancer, we can eliminate certain options based on their medical applications. Radioactive iodine-131 is specifically used to diagnose and treat thyroid cancer because the thyroid gland absorbs iodine to produce thyroid hormones. Due to iodine-131 decaying into xenon-131, xenon cannot be eliminated as it is a product of this decay, which may have its diagnostic applications. Strontium is used to ease the pain in bone cancers but is not specifically used to treat thyroid cancer. Thus, we can eliminate the following options: a) Helium, which has no known use in treating thyroid cancer, and d) Strontium, since its medical use is relevant to bone cancers, not thyroid. In the treatment of thyroid cancer, the radioactive atom commonly used is iodine-131. This isotope of iodine emits beta particles and gamma rays, making it effective in targeting thyroid cells. Helium is a non-radioactive gas and is not used for medical treatments. Xenon and strontium are also not typical choices for thyroid cancer treatment. Xenon is an inert gas, and strontium, while radioactive, is not commonly used for thyroid cancer. Therefore, based on what you now know, the possibilities that could be eliminated for treating thyroid cancer are a) Helium, c) Xenon, and d) Strontium. The correct answer is b) Iodine.