What results from the burning of powder inside a cartridge?

The correct answer is based on the fundamental principles of ballistics and the combustion process within a cartridge. When the gunpowder inside a cartridge ignites, it undergoes rapid combustion, which generates a significant amount of hot gases. These gases expand quickly and exert pressure on the bullet, pushing it down the barrel of the firearm.

This expansion of gases is critical to the operation of firearms, as it translates the chemical energy from the burning gunpowder into mechanical energy that propels the bullet. The rapid increase in volume and pressure from the expanding gases is what allows the bullet to reach high speeds as it exits the barrel.

While one might consider other options, cooling of the bullet does not occur as the reaction produces heat. Liquid formation is not a typical result of the combustion of solid propellant under normal conditions, and pressure release would imply a decrease in pressure rather than the rapid increase needed to propel a bullet. Understanding the expansion of gases helps clarify how firearms function and the effects of combustion during shooting.