1. The problem statement, all variables and given/known data Identify the element oxidized and the element reduced, in this chemical equation: H3AsO4+H2S ---> H3AsO3+S+H2O 2. Relevant equations none 3. The attempt at a solution So I have learned the rules for oxidation numbers: 1. The oxidation number of an element is always 0 regardless of its subscript. This is true as long as they are not part of compound. 2. The oxidation number of a simple ion is the charge of the ion. 3.The oxidation number of oxygen in compounds is -2. 4. The oxidation number of hydrogen in compounds is +1. 5.Group 1 and group 2 metals always have a +1, and +2 value, respectively, in compounds. 6. All other oxidation numbers are assigned so that the net sum of the oxidation numbers equals the net charge of the molecule or complex ion. So with what I know I can figure out the oxidation numbers for the oxygens and hydrogens in the chemical equation but how do I figure out the numbers for arsenic and sulfur?