Which one of the following statements about negative ions is incorrect?

Options

A. They are also known as anions.
B. They are formed when atoms gain electrons.
C. They are larger than the atom from which they were formed.
D. They are smaller than the atom from which they were formed.

Explanation

To determine which statement about negative ions is incorrect, we will analyze each option regarding their characteristics and formation.

### Step-by-Step Solution:

1. **Understanding Negative Ions (Anions)**:
- Negative ions are formed when an atom gains one or more electrons. This process results in a net negative charge due to the excess of electrons compared to protons.

2. **Analyzing the Statements**:
- **Option A**: "They are also known as anions."
- This statement is correct. Negative ions are indeed called anions.

- **Option B**: "They are formed when atoms gain electrons."
- This statement is also correct. Anions are formed specifically through the gain of electrons by neutral atoms.

- **Option C**: "C is larger than the atom from which they were formed."
- This statement is correct. When an atom gains an electron, the increased electron-electron repulsion causes the overall size of the ion (anion) to increase compared to the original atom.

- **Option D**: "They are smaller than the atom from which they were formed."
- This statement is incorrect. Anions are larger than the neutral atoms from which they are formed due to the addition of electrons and the resulting increase in electron-electron repulsion.

3. **Conclusion**:
- The incorrect statement about negative ions is Option D: "They are smaller than the atom from which they were formed."

### Final Answer:
The incorrect statement about negative ions is: **Option D: They are smaller than the atom from which they were formed.**

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