Final answer:
Gas pressure is caused by gas molecules colliding with the walls of their container; this effect is influenced by the temperature, volume, and the amount of gas present.
The correct answer is options 2) gas molecules colliding with vessel walls.
Step-by-step explanation:
Gas pressure is primarily caused by gas molecules colliding with the walls of their container. These collisions are described by the kinetic-molecular theory, which explains that the particles in gas move in random and straight lines until they collide elastically with one another or with the container walls.
The pressure exerted by a gas is therefore the result of these frequent collisions. It's also important to note that the pressure of a gas is influenced by factors such as the number of gas molecules (reflected in the moles of gas), the volume of the container, and the temperature of the gas.
Temperature affects gas pressure because an increase in temperature will increase the average kinetic energy and therefore the velocity of gas molecules, leading to more forceful collisions with the container walls.
Conversely, reducing the volume of a container increases the frequency of collisions with the walls, consequently increasing the pressure.
The correct answer is options 2) gas molecules colliding with vessel walls.