What is the purpose of the rubber stopper on a vial?

The purpose of the rubber stopper on a vial is primarily to seal the vial and maintain sterility. This is crucial in pharmaceutical practices, particularly in radiology, where medications often need to be free from contamination and maintain their efficacy. The rubber stopper creates an airtight barrier that prevents external contaminants, such as bacteria and particulate matter, from entering the vial. It also helps preserve the sterility of the medication until it is ready to be used, ensuring that the drug remains safe and effective for patient administration.

While other options may have their purposes in medication management, such as indicating the medication type or providing dosage information, these functions are not the primary role of the rubber stopper. The stopper's main function is its ability to safeguard the contents of the vial from environmental exposure, thereby ensuring the integrity of the medication inside.