On the HSK 7-9 vocabulary list, at CEFR level C2.

é ㄜˊ

    • to chant

ó ㄛˊ

    • oh (interjection indicating doubt or surprise)

ò ㄛˋ

    • oh (interjection indicating that one has just learned sth)

o ˙ㄛ

    • sentence-final particle that conveys informality, warmth, friendliness or intimacy
    • may also indicate that one is stating a fact that the other person is not aware of

Where 哦 is used

Sources