Lithium is the strongest reducing agent though it has highest ionisation enegy in its group. Which of the followinng factors is responsible for making Li the strongest reducing agent?

Options

A. Large heat of atomisation
B. Smaller size
C. Large subimation energy
D. Large amount of hydration enthalpy

Answer

To solve the question about why lithium is the strongest reducing agent despite having the highest ionization energy in its group, we can break down the reasoning step by step.

### Step-by-Step Solution:

1. **Understanding Reducing Agents**: A reducing agent is a substance that donates electrons in a chemical reaction and is oxidized in the process. The strength of a reducing agent is often related to its ability to lose electrons easily.

2. **Ionization Energy**: Ionization energy is the energy required to remove an electron from an atom. While lithium has the highest ionization energy in its group (alkali metals), this alone does not explain its strong reducing ability.

3. **Lithium's Electronic Configuration**: Lithium has the electronic configuration of 1s² 2s¹. When it loses one electron to form Li⁺, it achieves a stable noble gas configuration (1s²).

4. **Size of Li⁺ Ion**: The Li⁺ ion is very small compared to other alkali metal ions. The small size of the ion plays a crucial role in its properties.

5. **Hydration Energy**: Hydration energy is the energy released when ions are surrounded by water molecules. For smaller ions like Li⁺, the hydration energy is significantly higher because more water molecules can surround the ion due to its small size.

6. **Comparison with Other Alkali Metals**: Other alkali metals, while having lower ionization energies, do not have the same level of hydration energy as lithium. This means that when lithium loses an electron, the energy released from the hydration of Li⁺ compensates for the high ionization energy.

7. **Conclusion**: The strong reducing ability of lithium is attributed to its high hydration energy, which outweighs its high ionization energy. Therefore, in aqueous solutions, lithium is the strongest reducing agent due to the large amount of hydration enthalpy.

### Final Answer:
The factor responsible for making lithium the strongest reducing agent is the **large amount of hydration enthalpy**.

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