1. The problem is to calculate the oxidation number of an element in a compound. 2. The oxidation number (or state) is a measure of the degree of oxidation of an atom in a chemical compound. It is assigned based on a set of rules: - The oxidation number of an element in its elemental form is 0. - The oxidation number of a monatomic ion equals the charge of the ion. - Oxygen usually has an oxidation number of -2, except in peroxides where it is -1. - Hydrogen usually has an oxidation number of +1 when bonded to nonmetals and -1 when bonded to metals. - The sum of oxidation numbers in a neutral compound is 0; in a polyatomic ion, it equals the ion charge. 3. To calculate the oxidation number of a specific element, assign known oxidation numbers to other atoms and solve for the unknown using the sum rule. 4. For example, in H2SO4: - Hydrogen (H) is +1. - Oxygen (O) is -2. - Let sulfur (S) be x. 5. The sum of oxidation numbers is 0: $$2(+1) + x + 4(-2) = 0$$ 6. Simplify: $$2 + x - 8 = 0$$ 7. Solve for x: $$x = 8 - 2 = 6$$ 8. Therefore, the oxidation number of sulfur in H2SO4 is +6. This method applies generally to find oxidation numbers in compounds.