Final answer:
An atom with the electron configuration "He = 1s²" is diamagnetic because all its electrons are paired, leading to no net magnetic moment and a weak repulsion from a magnetic field.
Step-by-step explanation:
The magnetic property of an atom with the electron configuration "He = 1s²" is described as diamagnetic. This is because all the electrons in the helium atom are paired. According to the Pauli Exclusion Principle, the paired electrons have opposite spins, leading to the cancellation of their magnetic fields. Without unpaired electrons, the atom does not have a net magnetic moment and is not attracted into a magnetic field. In fact, due to its diamagnetism, the helium atom is weakly repelled by a magnetic field.