Among the following cations, the one present in a least ionic halide salt is

Options

A. Calcium ion
B. Barium ion
C. Caesium ion
D. Potassium ion

Answer

To determine which cation is present in the least ionic halide salt among the given options, we will follow these steps:

### Step 1: Understand the Concept of Ionic vs. Covalent Character
- Ionic character refers to the extent to which a bond between two atoms is ionic (i.e., involves transfer of electrons).
- Covalent character refers to the extent to which a bond is covalent (i.e., involves sharing of electrons).
- A bond with 100% ionic character has no covalent character, and vice versa.

**Hint:** Remember that the least ionic character means the bond has the highest covalent character.

### Step 2: Identify Factors Affecting Ionic and Covalent Character
- According to Fajans' rules, the covalent character of an ionic bond increases with:
1. Smaller size of the cation.
2. Larger size of the anion.
3. Higher positive charge on the cation.

**Hint:** Focus on the size and charge of the cations and anions involved.

### Step 3: Analyze the Given Cations
- The cations provided are:
- Ca²⁺ (Calcium)
- Ba²⁺ (Barium)
- Cs⁺ (Cesium)
- K⁺ (Potassium)

### Step 4: Compare the Sizes of the Cations
- As we move down a group in the periodic table, the size of the cations increases.
- Ca²⁺ is smaller than Ba²⁺.
- K⁺ is smaller than Cs⁺.

**Hint:** Smaller cations will have a higher charge density, which increases covalent character.

### Step 5: Compare the Charges of the Cations
- Ca²⁺ has a +2 charge, while K⁺ has a +1 charge. Ba²⁺ also has a +2 charge, and Cs⁺ has a +1 charge.
- Higher positive charge favors covalent character.

**Hint:** Higher positive charge leads to greater polarization of the anion.

### Step 6: Determine the Cation with the Least Ionic Character
- Between Ca²⁺ and K⁺, Ca²⁺ is smaller and has a higher charge, which favors covalent character.
- Between Ba²⁺ and Cs⁺, Ba²⁺ is smaller and has a higher charge than Cs⁺.
- Therefore, comparing Ca²⁺ and Ba²⁺, Ca²⁺ is smaller and has a higher charge than Ba²⁺.

### Conclusion
- The cation that is present in the least ionic halide salt is **Ca²⁺ (Calcium)**, as it exhibits the highest covalent character.

**Final Answer:** Calcium (Ca²⁺) is present in the least ionic halide salt.