The most acidic oxide formed by second period elements is

Cl, S are not second period elements;In second period, oxygen cannot have oxides;In second period,oxides of fluorine are unstable and cannot form oxo acids;HOF is a very unstable oxo acid;So nitrogen forms most acidic oxide;N2O5>CO2>B2O3>BeO>Li2O....acidic strength;In fact Li2O is basic and BeO is amphoteric;