In the context of the shared electron configuration you've described, when hydrogen shares electrons with oxygen, the outermost shell of the hydrogen atoms is full with 2 electrons (since each hydrogen atom can hold 2 electrons in its valence shell). For oxygen, which shares electrons with two hydrogen atoms, its valence shell becomes full with 8 electrons (accounting for its own 6 valence electrons plus the 2 shared electrons from hydrogen).
Therefore, the completed sentences would be:
"When hydrogen shares electrons with oxygen, the outermost shell of the hydrogen atoms are full with 2 electrons and oxygen’s valence shell is full with 8 electrons."