Molecular Orbital Theory
Valence Bond theories do not explain O2's magnetic nature, but, experiments do reveal that fact. The order in which O2 will fill its orbits is: sigma2s, sigma2s*, sigma2p, sigma2p*
Molecular Orbital Theory (MO) claims that O2 has unpaired electrons, and thus is magnetic, as liquid O2 sticks to a magnet. O2 has, in total, 12 valence electrons (each oxygen atom donating six).
MO theory is a method for determining molecular structure in which electrons are not assigned to individual bonds between atoms, but are treated as moving under the influence of the nuclei in the whole molecule.
Two electrons will fill each s orbital, while 6 electrons can occupy each p orbital. As per Exclusion Principle, 2 electrons will fill both the 2s and 2s* orbits, 6 electrons will fill the 2p orbital, and that leaves 2 electrons to fill the 2p* orbital.
These two electrons will only partially fill this orbital, and will have parallel spins. Since the rest of the electrons are all paired, the remaining two electrons in the 2p* orbital give the diatomic molecule a net total spin. It does not matter if they are +1/2 or -1/2 spins, they will both be the same. Since there is a net spin, O2 is paramagnetic.
The O2 in water molecules can be shaken to behave - like Iron atoms - as the magnetic material for (1) more of the same water (H2O) or for (2) molecules of any amino acid that contains O2 atoms in its chain.
The length + strength of the succussion determines the magnetism's strength, expressed in magnetic/gravitational units, called magravs.
The magravs strength of O2 varies according to the source of the O2 that it is released from. Magrav strength refers to the complementary force of magnetism (repulsion) and gravitation (attraction).
The O2 we inhale is a composite of all O2 magravs strength + composition of nature we are exposed to, like O2 of a certain tree, or shrub, or plant, varying also by its distance from the Earth's surface. Each with its own strength & composition.
Just as all elements in the physical universe have different isotopes, there are also many different magravs strength isotopes, or, in other words, many variations (forming a spectrum) in magravs strength.
The O2 in water in the atmosphere and in all the lakes have different composite strengths. Thus the water in a human body contains O2 of many different magravs.