Sodium vapour is paramagnetic, but cations of sodium are diamagnetic, while vapour magnesium as well as cations of magnesium are diamagnetic. Explain. 

Explanation

Atoms or ions with unpaired electrons are paramagnetic. Diamagnetism is due to the absence of unpaired electrons. Na vapour has unpaired electrons. Hence, paramagnetic. Number of electrons in `Na^(+)` is 10. They have no unpaired electrons. Hence, diamagnetic. Both Mg and `Mg^(2+)` have no unpaired electrons. Hence, they are diamagnetic.