Which statement defines the first ionisation energy of an element?
Choose your answer
The energy required to remove one electron from one atom in the gaseous state.
The energy required to remove one mole of electrons from one mole of atoms in the solid state.
The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions.
The energy required to remove one mole of electrons from one mole of gaseous 1+ ions.

