Final answer:
Oxygen molecules are paramagnetic and align with the magnetic field, while diatomic molecules such as nitrogen are diamagnetic and unaffected by the magnet.
Step-by-step explanation:
Paramagnetic substances are attracted to magnetic fields, while diamagnetic substances have a slight tendency to be repelled by magnetic fields. Oxygen molecules (Π2) contain unpaired electrons, making them paramagnetic. When poured through a magnet, the oxygen molecules line up with the magnetic field and stay suspended between the poles of the magnet where the magnetic field is strongest. On the other hand, diatomic molecules such as nitrogen (N₂) have no unpaired electrons and are diamagnetic, which means they are unaffected by the magnet.