Which is correct ?

Options

A. Ionic mobility in aqueous medium
`toLi^(+)ltNa^(+)ltK^(+)ltRb^(+)`
B. Covalant character
`toKClgtCaCl_(2)gtAlCl_(3)gtSnCl_(4)`
C. Boiling point order `toH_(2)OgtH_(2)TegtH_(2)S`
D. Dipole-dipole attraction `toKCl+H_(2)O`

Answer

To determine which statement is correct among the given options, we will analyze each statement step by step.

### Step 1: Analyze Ionic Mobility
1. **Statement 1**: The order of ionic mobility in aqueous solution is given as:
- Li⁺ > Na⁺ > K⁺ > Rb⁺

**Analysis**:
- Ionic mobility is influenced by the size of the ion and its hydration energy.
- As we move down the group of alkali metals (Li, Na, K, Rb), the size of the ions increases.
- Larger ions have lower hydration energy because they have a lower charge-to-size ratio.
- Therefore, Li⁺, being the smallest, has the highest hydration energy and the lowest ionic mobility.
- The correct order of ionic mobility should be:
- Rb⁺ > K⁺ > Na⁺ > Li⁺

**Conclusion**: Statement 1 is incorrect.

### Step 2: Analyze Covalent Character
2. **Statement 2**: The order of covalent character is given as:
- KCl < CaCl₂ < AlCl₃ < SnCl₂

**Analysis**:
- Covalent character increases with the charge and decreases with the size of the cation.
- K⁺ is larger than Ca²⁺, Al³⁺, and Sn⁴⁺, which means KCl should have the least covalent character.
- As the charge increases (Ca²⁺ to Al³⁺ to Sn⁴⁺), the covalent character should increase.
- The order presented does not reflect this trend.

**Conclusion**: Statement 2 is incorrect.

### Step 3: Analyze Boiling Points
3. **Statement 3**: The order of boiling points is given as:
- H₂O > H₂Te > H₂S

**Analysis**:
- Boiling points are influenced by intermolecular forces.
- H₂O has strong hydrogen bonding, leading to a high boiling point.
- H₂Te and H₂S have weaker van der Waals forces, but H₂Te is heavier than H₂S, which typically results in a higher boiling point due to increased mass.
- Therefore, the correct order should be:
- H₂O > H₂Te > H₂S

**Conclusion**: Statement 3 is correct.

### Step 4: Analyze Dipole-Dipole Interaction
4. **Statement 4**: The interaction between KCN and H₂O is described as dipole-dipole attraction.

**Analysis**:
- KCN dissociates into K⁺ and CN⁻ ions in water.
- The interaction between ions and polar molecules like water is termed ion-dipole interaction, not dipole-dipole.

**Conclusion**: Statement 4 is incorrect.

### Final Conclusion
- The only correct statement among the four provided is **Statement 3** regarding boiling points.