Which choice incorrectly identifies the oxidation number (o.n.) for the given species?

• A. In CO\(_2\), the oxidation number of carbon is +4.
• B. In Na\(_2\)SO\(_4\), the oxidation number of sulfur is +6.
• C. In NH\(_3\), the oxidation number of nitrogen is +3.
• D. In H\(_2\)O, the oxidation number of oxygen is -2.

Answer: (C)

Verified step by step guidance

1. Recall the rules for assigning oxidation numbers: the sum of oxidation numbers in a neutral molecule is zero, and in polyatomic ions, it equals the ion charge.
2. For CO\(_2\), assign oxygen an oxidation number of -2 (common for oxygen), then calculate carbon's oxidation number by setting the sum to zero: \(x + 2(-2) = 0\).
3. For Na\(_2\)SO\(_4\), assign sodium +1 (alkali metals), oxygen -2, then find sulfur's oxidation number by setting the sum to zero: \$2(+1) + x + 4(-2) = 0$.
4. For NH\(_3\), assign hydrogen +1, then calculate nitrogen's oxidation number by setting the sum to zero: \(x + 3(+1) = 0\).
5. For H\(_2\)O, assign hydrogen +1, oxygen is typically -2, verify by summing: \$2(+1) + (-2) = 0$. Identify which given oxidation number does not satisfy these conditions.