Paramagnetism refers to the magnetic state of a substance that possesses unpaired electrons. These unpaired electrons are free to align their spins in the presence of an external magnetic field which gives rise to a net magnetic moment, making the substance attracted to the magnetic field.

Option 1: Iron is ferrimagnetic, which is a stronger form of magnetism than paramagnetism.

Option 2: Hydrogen has no unpaired electrons (filled 1s orbital) and is thus diamagnetic, i.e., not attracted to a magnetic field.

Option 3: Oxygen is paramagnetic. It has two unpaired electrons in antibonding orbitals which generates a magnetic field in response to an external magnetic field.

Option 4: Nitrogen has all paired electrons (filled 2s and 2p orbitals) which makes it diamagnetic, similar to hydrogen.

So, the correct answer is oxygen which exhibits paramagnetism due to its unpaired electrons.