Because helium is lighter then the oxygen .and due to this helium gass carrier go upward easily .
Answer:
Anions. Some atoms have nearly eight electrons in their valence shell and can gain additional valence electrons until they have an octet. When these atoms gain electrons, they acquire a negative charge because they now possess more electrons than protons. Negatively charged ions are called anions.
Answer:
francium, caesium, helium
The answer above is correct (I took a test on this)
Answer: Argon (Ar), which has 18 protons.
