Carbon dioxide (\(\rm CO_{2}\)) can be collected in an open gas jar because it is denser than air(1.5 times heavier than air).

When \(\rm CO_{2}\) is released into the jar, it sinks to the bottom and displaces the lighter air above it. This property allows it to be collected by upward displacement of air, without the gas quickly escaping, making it easy to gather in an open container.