Select the correct statements .

Options

A. The heat of hydration of the dipositive earth metal ions increases
with an increase in their ionic size
B. Hydration of alkali metal ions is less than that of group 2
C. Alkaline earth metal ions because of their much larger charge to size ratio exert a much stronger electrostatic attaction on the oxygen of water molecule surrounding them .
D. Melting point of sodium halides is as follows `NaF gt NaCl gt NaBr gt NaI` .

Answer

To solve the question of selecting the correct statements regarding the heat of hydration and melting points of certain compounds, we will analyze each statement step by step.

### Step-by-Step Solution:

1. **Statement 1:** "The heat of hydration of di-positive earth metal ions increases with an increase in their ionic size."
- **Analysis:** The heat of hydration is influenced by the charge density, which is defined as the charge of the ion divided by its size (charge/size). For di-positive ions (like those from alkaline earth metals), as the ionic size increases, the charge density decreases. Since hydration energy is inversely proportional to size, an increase in size leads to a decrease in heat of hydration.
- **Conclusion:** This statement is **incorrect**.

2. **Statement 2:** "Hydration of alkali metal ions is less than that of group 2."
- **Analysis:** Alkali metals (group 1) have a +1 charge, while alkaline earth metals (group 2) have a +2 charge. The heat of hydration is directly proportional to the charge of the ion. Therefore, since group 2 ions have a higher charge, they will have a greater heat of hydration compared to alkali metal ions.
- **Conclusion:** This statement is **correct**.

3. **Statement 3:** "Alkaline earth metal ions, because of their much larger size ratio, exert a much stronger electrostatic attraction on oxygen or water."
- **Analysis:** The statement discusses the electrostatic attraction between alkaline earth metal ions and water. The larger charge of +2 for these ions compared to +1 for alkali metals results in a stronger electrostatic attraction, leading to higher hydration energy. The size ratio mentioned refers to the effective charge density, which supports the conclusion.
- **Conclusion:** This statement is **correct**.

4. **Statement 4:** "Melting point of sodium halides is as follows: NaF, NaCl, NaBr, NaI."
- **Analysis:** The melting points of sodium halides depend on the ionic character, which is influenced by the electronegativity difference between sodium and the halogen. As we move down the group of halogens (F, Cl, Br, I), the electronegativity decreases, leading to a decrease in ionic character and thus a decrease in melting point. The order given (NaF > NaCl > NaBr > NaI) is consistent with this trend.
- **Conclusion:** This statement is **correct**.

### Final Conclusion:
The correct statements are **2, 3, and 4**.