The sum of oxidation numbers of all atoms in an ion is zero.

Answer

To address the question, "The sum of oxidation numbers of all atoms in an ion is zero," we need to clarify the concept of oxidation numbers and how they relate to ions and neutral compounds.

### Step-by-Step Solution:

1. **Understanding Oxidation Numbers**:
- Oxidation numbers are assigned to atoms in a molecule or ion based on a set of rules. They help in determining the degree of oxidation or reduction of an element in a chemical reaction.

2. **Oxidation Numbers in Ions**:
- For ions, the sum of the oxidation numbers of all atoms is equal to the charge of the ion. This means that if an ion has a negative charge, the sum of the oxidation numbers will also be negative.

3. **Examples of Ions**:
- Take the sulfate ion (SO₄²⁻):
- Sulfur (S) has an oxidation number of +6.
- Each oxygen (O) has an oxidation number of -2.
- Therefore, the total oxidation number is:
\[ +6 + 4(-2) = +6 - 8 = -2 \]
- This matches the charge of the sulfate ion, which is -2.

4. **Other Ion Examples**:
- For the nitrate ion (NO₃⁻):
- Nitrogen (N) has an oxidation number of +5.
- Each oxygen has an oxidation number of -2.
- Total oxidation number:
\[ +5 + 3(-2) = +5 - 6 = -1 \]
- This matches the charge of the nitrate ion, which is -1.

5. **Neutral Compounds**:
- In a neutral compound, the sum of the oxidation numbers is zero. For example, in potassium nitrate (KNO₃):
- Potassium (K) has an oxidation number of +1.
- Nitrogen (N) has an oxidation number of +5.
- Each oxygen has an oxidation number of -2.
- Total oxidation number:
\[ +1 + 5 + 3(-2) = +1 + 5 - 6 = 0 \]
- This confirms that the sum of oxidation numbers in a neutral compound is zero.

6. **Conclusion**:
- The statement "The sum of oxidation numbers of all atoms in an ion is zero" is incorrect. For ions, the sum of oxidation numbers equals the charge of the ion, while for neutral molecules, the sum is zero.