The correct description for an atom of helium would be option C. An atom of helium has its valence electrons in its first energy level, it wouldn't and can't satisfy the Octet rule as it only has 2 electrons, but with 2, it has a full shell, as the first energy level can hold only 2 electrons.
1s2 2s2 2p2 i hope this helps
Note down the formula below

Mass of the compound

Mass % of Hydrogen:-



Mass % of Oxygen:-


