Question

Why gas fills the container easily???

Answer 1

Because the intermolecular force of attraction is negligible and intermolecular space is very large in gases.
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Answer 2

The atoms and molecules in gases are much more spread out than in solids or liquids. They vibrate and move freely at high speeds. A gas will fill any container, but if the container is not sealed, the gas will escape. Gas can be compressed much more easily than a liquid or solid.

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