Doomed fictional planet, 7 letters
Doomed planet of comics, 7 letters
Gas in fluorescent lamps, 7 letters
Green planet of the comics, 7 letters
Inert gaseous element, 7 letters
Its atomic number is 36, 7 letters
Kal-El's birthplace, 7 letters
Superman's birthplace, 7 letters
A colorless element that is one of the six inert gasses, 7 letters
Occurs in trace amounts in air, 7 letters
The length of a meter is based precisely on the amount of light emitted from this, 14 letters
Element in comic books since 1949, 10 letters
Fictional substance in Superman, 10 letters
Superhero's undoing, 10 letters