Answer: helium

AnswerCrossword Clue
HELIUM

Balloon gas

HELIUM

Second lightest element

HELIUM

Light element, and a hint to how the answers to starred clues have been inflated

HELIUM
Blimp filler
HELIUM
Voice-changing gas
HELIUM"Ashes" of the sun.
HELIUMVery light gas.
HELIUMInert gas.
HELIUMVery light, inert gas.
HELIUMGas
HELIUMBalloon filler
HELIUMScientific discovery of 1868
HELIUMParty-balloon filler
HELIUMBlimp supply
HELIUMParty balloon filler
HELIUMContents of party store tanks
HELIUMIt can raise your voice