An ionic compound `A^(+)B^(-)` is most likely to be formed when :

Options

A. the ionization energy of A is high and electron affinity of B is low
B. the ionization energy of A is low and electron affinity of B is high
C. both, the ionization energy of A and electron affinity of B are high
D. both, the ionization energy of A and electron affinity of B are low

Answer

To determine when an ionic compound \( A^+B^- \) is most likely to be formed, we need to consider the properties of the elements involved, specifically their ionization energy and electron affinity.

### Step-by-Step Solution:

1. **Understand Ionic Compounds**: Ionic compounds are formed when one atom donates an electron to another atom, resulting in the formation of cations (positively charged ions) and anions (negatively charged ions).

2. **Ionization Energy**: For the formation of a cation \( A^+ \), the ionization energy of element A must be low. This means that element A should have a larger atomic size, which allows it to lose an electron more easily due to the weaker attraction between the nucleus and the outermost electron.

3. **Electron Affinity**: For the formation of an anion \( B^- \), the electron affinity of element B must be high (more negative). This indicates that element B has a strong tendency to gain an electron, which is typically seen in elements with smaller atomic sizes, as they can attract electrons more effectively.

4. **Example Analysis**: Consider the example of cesium fluoride (CsF):
- **Cesium (Cs)**: It has a very large atomic size, resulting in low ionization energy. This allows it to easily lose an electron to form \( Cs^+ \).
- **Fluorine (F)**: It has a small atomic size and high electron affinity, allowing it to gain an electron easily to form \( F^- \).

5. **Conclusion**: Therefore, an ionic compound \( A^+B^- \) is most likely to be formed when:
- Element A has a low ionization energy (large atomic size).
- Element B has a high electron affinity (small atomic size).

### Final Answer:
An ionic compound \( A^+B^- \) is most likely to be formed when element A has a low ionization energy and element B has a high electron affinity.

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