HO VV =0 2 t 2 0 HO V 2 2 t V t V t 2 I+ 2S O 2I+SO 2 I+ 2NaS O → 2NaI+ Na SO 2 2 3 4 6 2 2 2 3 24 6 2− SO 2 3 2− SO 2 3