In the reaction 2 NH3 + 3 CuO → N2 + 3 Cu + 3 H2O, what are the oxidation numbers of nitrogen in NH3 (reactant) and N2 (product)?

• A. In NH3: -3; In N2: 0
• B. In NH3: -3; In N2: -2
• C. In NH3: +3; In N2: 0
• D. In NH3: 0; In N2: -3

Answer: (A)

Verified step by step guidance

1. Identify the oxidation state rules relevant to nitrogen and hydrogen in ammonia (NH3). Hydrogen generally has an oxidation number of +1 when bonded to nonmetals.
2. Assign the oxidation number of hydrogen as +1 in NH3. Since there are three hydrogens, the total positive charge contributed by hydrogen is +3.
3. Let the oxidation number of nitrogen in NH3 be x. The sum of oxidation numbers in a neutral molecule must be zero, so set up the equation: \(x + 3(+1) = 0\).
4. Solve the equation for x to find the oxidation number of nitrogen in NH3.
5. For N2, which is a diatomic molecule of the same element, the oxidation number of each nitrogen atom is zero because the atoms share electrons equally.