Answer: hydrogen

AnswerCrossword Clue
HYDROGEN

It's always number one

HYDROGEN

H

HYDROGEN

Most abundant element

HYDROGEN
Element in water
HYDROGEN
Light gas
HYDROGENRocket fuel component
HYDROGENLight element
HYDROGENLightest element
HYDROGENFocus of scientific limelight.
HYDROGENTypical univalent element.
HYDROGENElement of vast power.
HYDROGENElement potentially destructive.
HYDROGENThe lightest of all known substances.
HYDROGENLightest of all known substances.
HYDROGENLightest known substance
HYDROGENOne on a certain table
HYDROGENFirst item on a certain table