What is the oxidation number of each underlined element?
a) P₄                                  b) BO₃^3–                                c) AsO₄^2–                           d) HSO₄^–

• A. a) -3 b) +3 c) -2 d) -2
• B. a) -2 b) 0 c) -6 d) -6
• C. a) 0 b) +3 c) +6 d) +6
• D. a) 0 b) +3 c) -6 d) -6

Answer: (C)

Verified step by step guidance

1. Identify the oxidation number of phosphorus in P4: Since P4 is a molecule consisting of only phosphorus atoms, the oxidation number of each phosphorus atom is 0 because the molecule is in its elemental form.
2. Determine the oxidation number of boron in BO3^3-: The overall charge of the ion is -3. Oxygen typically has an oxidation number of -2. Set up the equation: x + 3(-2) = -3, where x is the oxidation number of boron.
3. Calculate the oxidation number of arsenic in AsO4^2-: The overall charge of the ion is -2. Oxygen has an oxidation number of -2. Set up the equation: x + 4(-2) = -2, where x is the oxidation number of arsenic.
4. Find the oxidation number of sulfur in HSO4^-: The overall charge of the ion is -1. Hydrogen has an oxidation number of +1, and oxygen has an oxidation number of -2. Set up the equation: 1 + x + 4(-2) = -1, where x is the oxidation number of sulfur.
5. Solve each equation to find the oxidation numbers: For BO3^3-, solve x - 6 = -3 to find x. For AsO4^2-, solve x - 8 = -2 to find x. For HSO4^-, solve 1 + x - 8 = -1 to find x.