(i) Higher be the positive oxidation value of non-metal oxide, higher be the acidic nature. (ii) For same value of oxidation number, more electronegative element associated with oxygen shows more acidic nature. Thus, correct order of acidic characteris N2O5>SO2>CO2>CO (+5)‌‌(+4)‌‌(+4)‌‌(+2) Note CO is a neutral oxide.