Some statements are given regarding nature of oxides
i) In second period, nitrogen form strongest acidic oxide
ii) In third period, sodium forms strongest basic oxide
iii)Oxides of metalloids are generally amphoteric in nature

Generally non-metal elements form acidic oxides whereas metal elements form basic oxides. Nitrogen, N forms strongest acidic oxide in the 3rd period. ${\text{Ex:\hspace{0.17em}N}}_{\text{2}}{\text{O}}_{\text{3}}{\text{,\hspace{0.17em}N}}_{\text{2}}{\text{O}}_{\text{5}}$ 
${\text{N}}_{\text{2}}{\text{O}}_{\text{5}}+{\text{\hspace{0.17em}H}}_{\text{2}}\text{O\hspace{0.17em}\hspace{0.17em}}\to 2{\text{HNO}}_{\text{3}}\left(\text{Strong\hspace{0.17em}Acid}\right)$
In the 3rd period, sodium Na forms strong basic oxide. Ex: ${\text{Na}}_{\text{2}}\text{O}$ 
${\text{Na}}_{\text{2}}\text{O\hspace{0.17em}}+{\text{\hspace{0.17em}H}}_{\text{2}}\text{O\hspace{0.17em}\hspace{0.17em}}\to 2\text{NaOH\hspace{0.17em}\hspace{0.17em}}\left(\text{Strong\hspace{0.17em}Base}\right)$