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All answers having "Light gas" as clue:

4 Character Answers:

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GATE

HAUL

NEON



5 Character Answers:

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ARGON

ETHER

XENON



6 Character Answers:

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HELIUM

KEEPUP



8 Character Answers:

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HYDROGEN



9 Character Answers:

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ALLOCATED



13 Character Answers:

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GORDONBENNETT