Among `CaH_2, BeH_2 , BaH_2`, the order of ionic character is

Options

A. `BeH_2 lt CaH_2 lt BaH_2`
B. `CaH_2lt BeH_2 lt BaH_2`
C. `BeH_2 lt BaH_2 lt CaH_2`
D. `BaH_2 lt BeH_2 lt CaH_2`

Explanation

To determine the order of ionic character among calcium hydride (CaH₂), beryllium hydride (BeH₂), and barium hydride (BaH₂), we can use Fajans' rules, which relate the size of the cation to its polarizing power and, consequently, its ionic character.

### Step-by-Step Solution:

1. **Understand Fajans' Rule**:
- According to Fajans' rule, the smaller the size of the cation, the greater its polarizing power. This means that smaller cations can distort the electron cloud of the anion (in this case, hydride ions, H⁻) more effectively, leading to a higher covalent character and a lower ionic character.

2. **Identify the Cations**:
- The cations we are dealing with are:
- Beryllium (Be²⁺)
- Calcium (Ca²⁺)
- Barium (Ba²⁺)

3. **Compare the Sizes of the Cations**:
- Beryllium (Be²⁺) is the smallest cation, followed by calcium (Ca²⁺), and barium (Ba²⁺) is the largest.
- Thus, the order of size is: Be²⁺ < Ca²⁺ < Ba²⁺.

4. **Determine Polarizing Power**:
- Since Be²⁺ is the smallest, it has the highest polarizing power, which means it will have the least ionic character (most covalent character).
- Ca²⁺ is next, having moderate polarizing power, leading to moderate ionic character.
- Ba²⁺, being the largest, has the least polarizing power, resulting in the highest ionic character.

5. **Establish the Order of Ionic Character**:
- Based on the polarizing power and size of the cations, we can conclude the order of ionic character:
- BaH₂ > CaH₂ > BeH₂
- Therefore, the order of ionic character from highest to lowest is: BaH₂ > CaH₂ > BeH₂.

### Final Answer:
The order of ionic character among CaH₂, BeH₂, and BaH₂ is:
**BaH₂ > CaH₂ > BeH₂**