Sodium vapour is paramagnetic, but cations of sodium are diamagnetic, while magnesium vapour 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
Number of electrons in Na is 11. Na vapour has unpaired electrons. Hence, paramagnetic.
Number of electrons in `Na^(+)` is 10. Na cations have no unpaired electrons. Hence, diamagnetic.
Both `Mg and Mg^(2+)` have no unpaired electrons. Hence, they are diamagnetic.