In an ionic compound `A^(+) X^(-)` the degree of covalent bonding is greatest when

Options

A. `A^(+) and X^(-)` ion are small
B. `A^(+)` is small and `X^(-)` is large
C. `A^(+) and X^(-)` ions are approximately of the same size
D. `X^(-)` is small and `A^(+)` is large

Answer

To determine when the degree of covalent bonding is greatest in the ionic compound \( A^+ X^- \), we can analyze the factors that influence covalent character in ionic compounds. The degree of covalent bonding is influenced by the size and charge of the ions involved, as described by Fajans' rules.

### Step-by-Step Solution:

1. **Understanding Ionic and Covalent Bonds**:
- Ionic bonds are formed through the transfer of electrons from one atom to another, resulting in the formation of cations and anions.
- Covalent bonds involve the sharing of electrons between atoms.

2. **Fajans' Rules**:
- According to Fajans' rules, the covalent character in an ionic bond increases when the cation is small and highly charged, and the anion is large and has a high polarizability.
- A small cation can distort the electron cloud of a larger anion, leading to a greater degree of covalent character.

3. **Analyzing the Ions**:
- In the compound \( A^+ X^- \):
- \( A^+ \) is the cation (positive ion).
- \( X^- \) is the anion (negative ion).
- For maximum covalent character:
- The cation \( A^+ \) should be small (high charge density).
- The anion \( X^- \) should be large (high polarizability).

4. **Conclusion**:
- Therefore, the degree of covalent bonding in the ionic compound \( A^+ X^- \) is greatest when \( A^+ \) is a small cation and \( X^- \) is a large anion.

### Final Answer:
The degree of covalent bonding in the ionic compound \( A^+ X^- \) is greatest when \( A^+ \) is a small cation and \( X^- \) is a large anion.

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