To determine whether the statement "An anion is larger than a cation if they are iso-electronic" is true or false, we can analyze the concepts of ionic size, isoelectronic species, and the effects of charge on atomic size.
### Step-by-Step Solution:
1. **Understanding Isoelectronic Species**:
- Isoelectronic species are atoms or ions that have the same number of electrons. For example, Na⁺ (sodium ion) and F⁻ (fluoride ion) both have 10 electrons.
2. **Formation of Cations and Anions**:
- A cation is formed when an atom loses one or more electrons. For instance, sodium (Na) loses one electron to form Na⁺.
- An anion is formed when an atom gains one or more electrons. For example, fluorine (F) gains one electron to form F⁻.
3. **Effect of Charge on Size**:
- When an atom loses an electron to form a cation, the remaining electrons experience a stronger effective nuclear charge (the pull from the nucleus), which causes the electron cloud to contract. Thus, cations are smaller than their parent atoms.
- Conversely, when an atom gains an electron to form an anion, the added electron increases electron-electron repulsion and reduces the effective nuclear charge experienced by the remaining electrons. This causes the electron cloud to expand. Therefore, anions are larger than their parent atoms.
4. **Comparing Sizes of Isoelectronic Cations and Anions**:
- In the case of isoelectronic species (like Na⁺ and F⁻), the anion (F⁻) has gained an electron, leading to increased size due to electron-electron repulsion. The cation (Na⁺), having lost an electron, is smaller due to the increased effective nuclear charge acting on the remaining electrons.
- Therefore, when comparing an anion and a cation that are isoelectronic, the anion will always be larger than the cation.
5. **Conclusion**:
- Since we have established that an anion is indeed larger than a cation when they are isoelectronic, the statement is **True**.
### Final Answer:
The statement "An anion is larger than a cation if they are iso-electronic" is **True**.
