O3 of N and P,P2O3 (P4O6, dimer of P2O3) are purely acidic, that of As(As4O6, dimer of As2O3) and Sb(Sb4O6, dimer of Sb2O3 ) amphoteric and that of Bi(Bi2O3) is predominantly basic. The oxides of the type
+3
E2
O5 are more acidic, e.g. N2O5,P2O5,As2O5,Sb2O5 So, in the given set of oxides of group- 15 elements, two oxides are amphoteric, As4O6 and Sb4O6