Q.What happens when magnesium metal is burnt in air?

Group 2 elements (Be, Mg, Ca, Sr, Ba, Ra) have electronic configuration $ns^2$ and lose both valence electrons to give $M^{2+}$ ions. Compared with the alkali metal in the same period, an alkaline earth atom has one more proton and one fewer electron shell relative to size, so it is smaller and has a noticeably higher first and second ionisation enthalpy; this makes Group 2 hydroxides and oxides distinctly less basic than the corresponding Group 1 hydroxides/oxides in the same period, e.g. $Mg(OH)_2$ is weaker as a base than $NaOH$. Down the group, however, atomic/ionic size increases and ionisation enthalpy falls steadily, so basic character of the oxides and hydroxides increases from Be to Ba: $BeO$/$Be(OH)_2$ are amphoteric while $BaO$/$Ba(OH)_2$ are strongly basic and appreciably soluble. Overa …