Question

when gases are added to a container... the gas particles remain clustered together. the gas particles individually decrease in size to take up less space in the container. the gas particles spread out to fill the container. the gas particles individually increase in size to fill the container.

Explanation:

Gases have weak intermolecular forces and high kinetic energy, allowing particles to spread out and fill the available space of a container. They don't cluster together, and the size of individual gas - particles doesn't change to fill the container.

Answer:

the gas particles spread out to fill the container.