The reducing power of a metal depends on various factors. Suggest the factor which makes Li, the strongest reducing agent in aqueous solution.

Options

A. Sublimation enthalpy
B. Ionisation enthylpy
C. Hydration enthalpy
D. Electron-gain enthalpy

Explanation

To determine why lithium (Li) is the strongest reducing agent in aqueous solution, we need to analyze the factors that influence the reducing power of metals. Here’s a step-by-step breakdown of the reasoning:

### Step 1: Understanding Reducing Agents
A reducing agent is a substance that donates electrons in a chemical reaction and becomes oxidized. The strength of a reducing agent is influenced by its ability to lose electrons easily.

**Hint:** Consider the properties of the metal and how they affect its ability to lose electrons.

### Step 2: Ionization Enthalpy
The ionization enthalpy is the energy required to remove an electron from an atom in the gaseous state. Lithium has a relatively high ionization enthalpy compared to other alkali metals, which means it holds onto its electrons more tightly.

**Hint:** Think about how the energy required to remove an electron affects the reducing ability.

### Step 3: Size of the Lithium Ion
Lithium ion (Li⁺) is small in size compared to other alkali metal ions. This small size allows it to have a high charge density, which leads to strong interactions with water molecules.

**Hint:** Reflect on how the size of an ion can influence its interactions with solvent molecules.

### Step 4: Hydration Energy
When lithium ion is dissolved in water, it is surrounded by water molecules. The small size of the Li⁺ ion allows for a greater number of water molecules to surround it, leading to a significant release of hydration energy. This hydration energy is the energy released when water molecules surround and stabilize the ion in solution.

**Hint:** Consider how the energy released during hydration can affect the stability of the ion in solution.

### Step 5: Conclusion
The large amount of hydration energy released when Li⁺ is formed in aqueous solution compensates for its high ionization enthalpy. This makes lithium a very effective reducing agent because the energy released helps to stabilize the ion, allowing it to more readily donate electrons.

**Final Answer:** The factor that makes lithium the strongest reducing agent in aqueous solution is its high hydration energy due to its small ionic size.

### Summary
1. Reducing agents donate electrons.
2. Lithium has a high ionization enthalpy.
3. The small size of Li⁺ allows for strong hydration.
4. Large hydration energy release stabilizes Li⁺.
5. Thus, lithium is the strongest reducing agent in aqueous solution.