Which of the following is most commonly used on cattle to insert an oral medication?

The balling gun is the most commonly used device for inserting oral medications in cattle because it is specifically designed to administer large pills or boluses directly into the animal's throat. This tool helps ensure that the medication reaches the esophagus without causing discomfort or injury to the animal. It is particularly effective for delivering medications that come in bolus form, which are often used for their sustained release or specific therapeutic effects.

While other tools like the drench gun are also utilized, they are more suited for administering liquid medications rather than solid forms. A scalpel is an instrument for making incisions or surgical procedures, and it has no role in the administration of oral medications. Similarly, a hypodermic syringe is used for injections rather than oral delivery, making it unsuitable for this purpose. Thus, the balling gun stands out as the optimal choice for oral medication delivery in cattle.