Identify the correct statement from the following

Options

A. The order of hydration enthapies of alkaline earth cations
`Be^(2+)ltMg^(2+)ltCa^(2+)ltSr^(2+)ltBa^(2+)`
B. Lithium and magnesium show some similarities in their physical properties as they are diagonally placed in periodic table
C. Lithium is softer among all alkali metals
D. Lithium chloride is deliquescent and crystallises as a hydrate, LiCl.`H_2O`

Answer

To solve the question of identifying the correct statement from the given options, we will analyze each option step by step.

### Step 1: Analyze Option 1
**Statement**: The order of hydration enthalpies of alkaline earth cations is increasing down the group.

**Explanation**:
- Alkaline earth cations include Be²⁺, Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺.
- As we move down the group, the size of the cations increases due to the addition of electron shells.
- A smaller cation (like Be²⁺) has a higher charge density and can attract water molecules more effectively than larger cations (like Ba²⁺).
- Therefore, the hydration enthalpy decreases down the group, making this statement incorrect.

### Step 2: Analyze Option 2
**Statement**: Lithium and Magnesium show some similarity in physical properties as they are diagonally placed in the periodic table.

**Explanation**:
- Lithium (Li) is in Group 1, and Magnesium (Mg) is in Group 2.
- They are diagonally placed in the periodic table, which often leads to similarities in properties.
- Both elements exhibit similar electronegativities and form hydroxides that are weak bases.
- They also form similar compounds with nitrogen and have comparable hardness.
- Thus, this statement is correct.

### Step 3: Analyze Option 3
**Statement**: Lithium is soft among alkali metals.

**Explanation**:
- Alkali metals include Li, Na, K, Rb, and Cs.
- Among these, lithium is actually one of the harder alkali metals due to its smaller size and stronger attraction between the nucleus and its outermost electron.
- Therefore, this statement is incorrect.

### Step 4: Analyze Option 4
**Statement**: Lithium chloride is deliquescent and crystallizes as the hydrate LiCl.H2O.

**Explanation**:
- Deliquescent substances absorb moisture from the air.
- LiCl is indeed deliquescent due to the small size of Li⁺, which allows it to attract water molecules.
- However, LiCl typically crystallizes as LiCl.2H2O, not LiCl.H2O.
- Hence, this statement is also incorrect.

### Conclusion
After analyzing all the options, the correct statement is **Option 2**: "Lithium and Magnesium show some similarity in physical properties as they are diagonally placed in the periodic table."

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