Final answer:
Barium sulfate (BaSO4), used as a radiopaque contrast media for medical imaging, is a nontoxic substance because of its low solubility in water. It coats the digestive tract and provides contrast for clear imaging, thus it is classified as an ionic compound.
Step-by-step explanation:
Barium sulfate (BaSO₄) is indeed used in imaging techniques as a radiopaque contrast media. Its effectiveness in medical imaging, such as x-ray examination or CT scans, is due to its ability to coat the esophagus, stomach, or intestine without being absorbed by the body. This characteristic makes it extremely valuable for visualizing diseased or damaged areas within these organs. Given its composition, barium sulfate is best classified as a ionic compound. The Ba2+ (barium) cations and the SO42- (sulfate) anions form an ionic lattice that is poorly soluble in water. This low solubility ensures that the compound will precipitate rather than dissolve when ingested, allowing it to coat the digestive tract and provide the necessary contrast for imaging purposes.