2. Определите валентность по формулам: Fe2O3, MnO, Ag2O, HCl, Na2S, Ca3N2, P2O5, Mg2O7, NO2.

1. Fe2O3 (Fe-III, O-II), MnO (Mn-II, O-II), Ag2O (Ag-I, O-II), HCl (H-I, Cl-I), Na2S (Na-I, S-II), Ca3N2 (Ca-II, N-III), P2O5 (P-V, O-II), Mg2O7 (Mg-II, O-II), NO2 (N-IV, O-II).