What is defined as a device that fires a projectile using an explosive charge?

In the context of this question, a device that fires a projectile using an explosive charge is accurately defined as a firearm. Firearms operate by combusting a cartridge or shell, initiating an explosive reaction that propels a projectile (such as a bullet) down a barrel and out towards a target. This is a fundamental characteristic of firearms, distinguishing them from other types of projectile devices.

The other choices represent different types of projectile-launching devices that do not utilize an explosive charge. For instance, a crossbow utilizes a drawn bowstring to launch bolts but does not employ an explosive mechanism. Similarly, a slingshot relies on elastic tension to hurl stones or other projectiles, while a bow and arrow operates through the energy stored in the bent limbs of the bow, without any explosive components. Consequently, the definition of a firearm specifically encompasses devices that function through explosive charges, making this answer the most accurate.