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 among all ements
D. `LiCl and MgCl_(2)` are most ionic in their groups

Answer

To determine the incorrect statement among the given options, let's analyze each option step by step:

### Step 1: Analyze Option 1
**Statement:** Be²⁺ has larger hydration energy among alkaline earth metals.

- **Explanation:** Beryllium (Be) is the smallest alkaline earth metal. Hydration energy is inversely proportional to the size of the ion; smaller ions have higher hydration energy. Since Be²⁺ is small, it indeed has the largest hydration energy among alkaline earth metals.
- **Conclusion:** This statement is correct.

### Step 2: Analyze Option 2
**Statement:** Second ionization enthalpies of alkaline earth metals are smaller than those of the corresponding alkali metals.

- **Explanation:** Alkaline earth metals have the general electronic configuration of ns², while alkali metals have ns¹. After the first ionization, alkali metals become ns⁰ (noble gas configuration), which is stable and thus requires more energy to remove another electron. In contrast, alkaline earth metals become ns¹ after the first ionization, making it easier to remove the second electron. Therefore, the second ionization enthalpy of alkaline earth metals is greater than that of alkali metals.
- **Conclusion:** This statement is incorrect.

### Step 3: Analyze Option 3
**Statement:** Li is the strongest reducing agent among all the elements due to highest hydration energy.

- **Explanation:** Lithium (Li) is indeed a strong reducing agent because it is small in size and has high hydration energy, allowing it to easily lose its outer electron. This property contributes to its strong reducing ability.
- **Conclusion:** This statement is correct.

### Step 4: Analyze Option 4
**Statement:** LiCl and MgCl₂ are most ionic in their groups.

- **Explanation:** While MgCl₂ is ionic, LiCl is not purely ionic; it has significant covalent character due to the small size and high polarizing power of Li. Therefore, it is incorrect to say that LiCl is the most ionic in its group.
- **Conclusion:** This statement is incorrect.

### Final Conclusion
The incorrect statements are found in Options 2 and 4. However, since the question asks for one incorrect statement, we can conclude that:

**The incorrect statement is Option 2: "Second ionization enthalpies of alkaline earth metals are smaller than those of the corresponding alkali metals."**