2. Определите валентность по формулам: CaO, Mn2O5, Al2S3, SO2, MnO, Na2O, HI, NH3, H2S.

1. CaO (Ca-II, O-II), Mn2O5 (Mn-V, O-II), Al2S3 (Al-III, S-II), SO2 (S-IV, O-II), MnO (Mn-II, O-II), Na2O (Na-I, O-II), HI (H-I, I-I), NH3 (N-III, H-I), H2S (H-I, S-II).