atomic number 2

Từ điển WordNet v3.1 - WordNet Dictionary

noun

a very light colorless element that is one of the six inert gasses;
the most difficult gas to liquefy;
occurs in economically extractable amounts in certain natural gases (as those found in Texas and Kansas)
• Syn:
helium, He
• Hypernyms:
chemical element, element, noble gas, inert gas, argonon