it means two oxygen atoms
To completely describe an electron in an atom, four quantum numbers are needed: energy (n), angular momentum (ℓ), magnetic moment (mℓ), and spin (ms). The first quantum number describes the electron shell, or energy level, of an atom.
The moon surface is
visible to an observer on earth due to the gravitational force that attracts the
moon to the earth. The more massive the body is, the more the smaller body is
attracted to the larger body. We can only see the side of the moon due to the
speed at which the moon rotates.