In which of the following is the oxidation number of sulphur equal to -2?

The oxidation number of an element is a number that represents the number of electrons that an atom has gained or lost. In the case of sulfur, it can have different oxidation numbers depending on the compound it is present in. When the oxidation number of sulfur is -2, it means that sulfur has gained two electrons. So, we need to identify the compound in which sulfur has an oxidation number of -2. Out of the given options, only the second option - H2S - contains sulfur with an oxidation number of -2. In H2S, hydrogen has an oxidation number of +1 and sulfur has an oxidation number of -2, which makes the overall charge of the compound neutral. In the other options: - S8 is a form of elemental sulfur and has an oxidation number of 0 since it is uncombined. - SO2 contains sulfur with an oxidation number of +4. - SO32- contains sulfur with an oxidation number of +4. Therefore, the correct answer is the second option - H2S.