Which of the following is an incorrect statement?

Options

A. The heats of hydration of the dipositive alkaline earth metal ions decrease with an increase in their ionic size
B. `NaNO_(3)` forms `Na_(2)O` on heating
C. Hydration of alkali metal ion is less than that of IIA group
D. Alkaline earth metal ions, because of their much larger charge to size ratio, exert a much stronger electrostatic attraction on the oxygen of water molecule surrounding them

Answer

To determine which of the provided statements is incorrect, we will analyze each statement one by one based on our understanding of the properties of s-block elements, particularly focusing on alkaline earth metals and their compounds.

### Step-by-Step Solution:

1. **Examine the First Statement:**
- **Statement:** "The heats of hydration of the dipositive alkaline earth metal ions decrease with an increase in their ionic size."
- **Analysis:** Hydration energy is inversely proportional to the size of the ion. As the size of the ion increases, the hydration energy decreases because larger ions attract fewer water molecules. Thus, this statement is **correct**.

2. **Examine the Second Statement:**
- **Statement:** "NaNO3 forms Na2O on heating."
- **Analysis:** When sodium nitrate (NaNO3) is heated, it decomposes to form sodium nitrite (NaNO2) and oxygen (O2), not sodium oxide (Na2O). Therefore, this statement is **incorrect**.

3. **Examine the Third Statement:**
- **Statement:** "Hydration of alkali metal ions is less than that of second A group."
- **Analysis:** Alkali metal ions (Group 1) have a lower charge density compared to alkaline earth metal ions (Group 2). As a result, alkali metal ions are surrounded by fewer water molecules than alkaline earth metal ions, making this statement **correct**.

4. **Examine the Fourth Statement:**
- **Statement:** "Alkaline earth metal ions because of their much larger charge to size ratio exert a much stronger electrostatic attraction on the oxygen of water molecules surrounding them."
- **Analysis:** Alkaline earth metal ions have a higher charge to size ratio compared to alkali metals, leading to a stronger attraction to water molecules. This statement is also **correct**.

### Conclusion:
Based on the analysis above, the **incorrect statement** is the second one: "NaNO3 forms Na2O on heating."