The incorrect statement is

Options

A. `Be^(2+)` cation has largest hydration energy among alkaline earth metal
B. The second ionisation enthalpies of alkaline earth metal are smaller than those of the corresponding alkali metals
C. Li is the strongest reducing agent in sol among all elments
D. `LiCl and MgCl_(2)` are most ionic in their groups

Answer

To determine the incorrect statement from the given options regarding alkali earth metals and their properties, we will analyze each statement step by step.

### Step 1: Analyze Statement A
**Statement A:** Beryllium cation has the largest hydration energy among all alkali earth metals.

- **Explanation:** Hydration energy generally decreases down the group in the periodic table. Beryllium, being at the top of the group, has the highest charge density and thus the largest hydration energy compared to other alkali earth metals like magnesium, calcium, strontium, barium, and radium.
- **Conclusion:** This statement is **correct**.

### Step 2: Analyze Statement B
**Statement B:** The second ionization enthalpy of alkali earth metals is smaller than those of corresponding alkali metals.

- **Explanation:** Alkali metals have a single electron in their outermost shell, and upon losing one electron, they attain a noble gas configuration. The second ionization energy for alkali metals is higher because it involves removing an electron from a stable noble gas configuration. In contrast, alkali earth metals have two electrons in their outermost shell, and the second ionization energy is relatively lower than that of alkali metals.
- **Conclusion:** This statement is **correct**.

### Step 3: Analyze Statement C
**Statement C:** Lithium is the strongest reducing agent in solution among all elements.

- **Explanation:** In aqueous solution, lithium is indeed a strong reducing agent due to its high standard reduction potential and low ionization energy. However, in the gas phase, cesium is a stronger reducing agent due to its larger atomic size and lower ionization energy.
- **Conclusion:** This statement is **correct** in the context of aqueous solutions.

### Step 4: Analyze Statement D
**Statement D:** Lithium chloride and magnesium chloride are the most ionic in their group.

- **Explanation:** Ionic character increases down the group due to the decrease in lattice energy and increase in size of the ions. Therefore, lithium chloride (LiCl) does not have the highest ionic character; rather, cesium chloride (CsCl) has the highest ionic character among alkali metal chlorides, and barium chloride (BaCl2) among alkali earth metal chlorides.
- **Conclusion:** This statement is **incorrect**.

### Final Answer
The incorrect statement is **Statement D**: Lithium chloride and magnesium chloride are the most ionic in their group.

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