the oxide in higher oxidation state of the element is more acidic than that of lower oxidation state,, why?????

In the case of a lower oxide of an element, the atom has a low oxidation state. This means that some of the valence electrons of the metal atom are not involved in bonding. The atom in lower oxidation state therefore is not electron deficient. As a result, it can donate electrons and behave as a base.

On the other hand, in the case of a higher oxide, an atom has a high oxidation state. This means that more number of valence electrons are involved in bonding and so, they are unavailable. In other words, it has less electrons available in its valence shell and is electron deficient. As a result, it can accept electrons and behave as an acid.