Please choose the correct answer to the question: On the periodic table, the elements in group 18 (8A) (helium, neon, argon, etc.) are grouped together because

Answer1: they are lighter than air. Answer2: they have full outer electron shells. Answer3: they have excess electrons to share. Answer4: they easily react with other elements.

Answer format: answer1/answer2/answer3/answer4
Answer: answer2