Which of the following is the strongest reducing agent in aqueous medium?

Options

A. `Mg`
B. `Na`
C. `Li`
D. `Ca`

Explanation

To determine which of the following is the strongest reducing agent in an aqueous medium, we can follow these steps:

### Step 1: Understanding Reducing Agents
A reducing agent is a substance that donates electrons to another substance and is itself oxidized in the process. In aqueous solutions, the strength of a reducing agent can be influenced by its enthalpy of hydration and ionization energy.

**Hint:** Remember that a stronger reducing agent will have a greater tendency to lose electrons.

### Step 2: Analyzing the Candidates
We need to evaluate the reducing agents provided in the question. Common candidates for reducing agents in aqueous solutions include alkali metals (like Li, Na, K) and some other metal ions.

**Hint:** Look for the elements that are known to easily lose electrons.

### Step 3: Evaluating Enthalpy of Hydration and Ionization Energy
In aqueous solutions, the enthalpy of hydration (the energy released when ions are solvated by water) plays a significant role. A high negative enthalpy of hydration can compensate for a high ionization energy, making the element a strong reducing agent.

- **Lithium (Li)** has a high negative enthalpy of hydration, which compensates for its relatively high ionization energy compared to other alkali metals.

**Hint:** Compare the hydration energies of the candidates to see which one has the most favorable conditions for reduction.

### Step 4: Conclusion
Based on the analysis, Lithium (Li) emerges as the strongest reducing agent in aqueous medium due to its high negative enthalpy of hydration compensating for its high ionization energy.

**Final Answer:** The strongest reducing agent in aqueous medium is **Lithium (Li)**.

### Summary of Steps:
1. Understand what a reducing agent is.
2. Identify the candidates for reducing agents.
3. Evaluate the enthalpy of hydration and ionization energy.
4. Conclude that Lithium (Li) is the strongest reducing agent.