Final answer:
When a gas in a fixed-volume cylinder is heated and additional gas is added, the pressure of the gas will most likely increase due to more frequent and forceful collisions of gas molecules with the container's walls.
Step-by-step explanation:
The question is about what will happen to the pressure of the gas inside a cylinder when it is heated and additional gas is added. According to the principles of gas laws, specifically the combined gas law, which is related to pressure (P), volume (V), and temperature (T) of a gas, the pressure of the gas will increase if the temperature of the gas increases while the volume remains constant.
When the number of gas molecules is increased in a fixed volume, there is less space for the molecules to move, which means they will collide with the walls of the container more frequently, leading to an increase in pressure. Additionally, heating the gas will increase the kinetic energy of the molecules, resulting in more forceful collisions and therefore an increase in pressure.