If I understand correctly your question, you want to know why after oxidation of some elements, melting/boiling points of the corresponding oxides are higher or lower than the initial elements, right ? It is due to the molecular or covalent character of the resultant oxide: low melting/boiling points for covalent oxides (ex CO2 is a gas, WO3 is a volatile oxide, Mn2O7 is a liquid, etc), but high melting/boiling points for ionic oxides (ex Na2O melts at a much higher temperature than Na, same for MnO, etc.). High oxidation states lead to more covalent oxide, low oxidation states lead to more ionic oxides.

Hope it helps,

Alain

Yes that my Question.Please can you send me some reference literature to improve my knowledge about this .