According to Fajan rule, the covalent bond is favored by :

Options

A. Large cation and small anion
B. Large cation and large anion
C. Small cation and small anion
D. Small cation and large anion:

Explanation

To solve the question regarding Fajan's rule and the conditions that favor covalent bond formation, we can break down the explanation into clear steps.

### Step-by-Step Solution:

1. **Understand Fajan's Rule**: Fajan's rule provides criteria for determining the covalent character of ionic bonds. It states that certain conditions favor the formation of covalent bonds in what are typically ionic compounds.

2. **Identify the Size of Ions**: According to Fajan's rule, the size of the ions plays a crucial role:
- **Cation Size**: The cation should be **small**. A smaller cation has a higher charge density, which can polarize the electron cloud of the anion more effectively.
- **Anion Size**: The anion should be **large**. A larger anion has a more diffuse electron cloud, making it easier for the cation to induce polarization.

3. **Consider the Charge of Ions**: The charge on the ions also affects the covalent character:
- **High Charge**: Both the cation and anion should have a **high charge**. A higher charge increases the electrostatic attraction between the ions, enhancing the polarization effect.

4. **Conclusion**: Based on Fajan's rule, the conditions that favor covalent bond formation are:
- A **small cation** and a **large anion** with **high charges** on both ions.

5. **Final Answer**: Therefore, according to Fajan's rule, a covalent bond is favored by a small cation and a larger anion.