Reasoning: Oxidation numbers are bookkeeping values assigned to atoms assuming ionic character. The algebraic sum must equal the actual net charge of the ion.

Reasoning: In SO₄²⁻, 4 oxygens contribute - 8 total; to get - 2 overall charge, sulfur must be + 6, not + 8. The correct reasoning depends on sum equaling ion charge.

Reasoning: Oxygen contributes - 6 [3×(-2)]. To make total charge - 1, nitrogen must be + 5 so that + 5+(- 6)=- 1.

Reasoning: Oxidation numbers are assigned so that their sum matches the actual charge, ensuring consistency in redox accounting.

Reasoning: 4 hydrogens give + 4 total. Since ion charge is + 1, nitrogen must be - 3 so that - 3+4=+ 1.

Reasoning: In CO₃²⁻, total must equal - 2. Oxygen contributes - 6, so carbon must be + 4, not + 2.

Reasoning: Oxygen =- 6 total. Since ion charge is - 2, X₂ must contribute + 4 to balance (- 6+4=- 2).

Reasoning: Neutral molecules sum to zero; ions have net charge, so oxidation numbers sum to that charge.

Reasoning: Incorrect oxidation states break the rule that sum must equal - 2, showing the assignment is invalid.

Reasoning: Only NH₄⁺ gives correct sum: - 3+4(+ 1)=+ 1

Reasoning: Let, X+(-10)=-3 ⟹ X=+ 7

Reasoning: The key rule is algebraic sum equals the net ionic charge.

Reasoning: Oxygen =- 8 total ; P must be + 5 so sum =- 3.

Reasoning: Oxidation numbers are assigned based on assumed complete electron transfer for bookkeeping.

Reasoning: By definition, oxidation numbers always sum to the ion’s net charge.

Reasoning: Single atom ion oxidation number equals its charge.

Reasoning: CO₃²⁻ must sum to - 2, not + 2, so it violates the rule.

Reasoning: It allows calculation of unknown oxidation numbers using charge balance.