What is the chemical formula of the common contrast media agent "Barium"?

The correct answer, Barium sulfate, is widely used as a contrast agent in various medical imaging procedures, particularly in radiology for imaging the gastrointestinal tract. This compound is favored for its properties that make it suitable for contrast studies—it is insoluble in water, which minimizes the risk of systemic absorption and potential toxicity. The sulfate ion forms a stable suspension when mixed with a liquid, allowing for effective visualization of the gastrointestinal organs during X-ray examinations.

In contrast, the other compounds listed do not possess the same qualities that make Barium sulfate suitable for this purpose. For instance, Barium carbonate and Barium chloride are soluble in water and may present risks if absorbed into the bloodstream during a procedure. Barium hydroxide also does not serve as a contrast agent, as its chemical behavior is different, and it can react with acids rather than being inert and safe for use in imaging. Barium sulfate's unique properties ensure it is the optimal choice for patients undergoing imaging studies.