Large difference between the melting and boiling points of oxygen and sulphur can be explained.

Explanation

Due to small atomic size and high electronegativity, oxygen atom prefers to form `p pi-p pi` double bond with other oxygen atom forming diatomic oxygen `(O_(2))` molecule. In contrast due to bigger size and lower electronegativity, sulphur atom does not form `p pi-p pi` double bond with other sulphur atoms and hence does not exist as diatomic `(S_(2))` molecule. Instead, it prefers to form single bonds with other sulphur atoms. In other words, sulphur atom shows greater tendency for catenation than oxygen atom and hence exists as octa-atomic sulphur `(S_(8))` molecule. Due to much larger molecular size of `S_(8)` molecule as compared to `O_(2)` molecule, the van der Waals forces of attraction are much stronger in `S_(8)` molecules than in `O_(2)` molecules. As a result, there is a larger difference between the melting and boiling points of oxygen and sulphur.