Weak reductant in alkali metal is-

Options

A. `Li`
B. `Na`
C. K
D. `Cs`

Answer

To determine the weak reductant among alkali metals, we can follow these steps:

### Step 1: Identify the Alkali Metals
Alkali metals belong to Group 1 of the periodic table. The elements in this group include:
- Lithium (Li)
- Sodium (Na)
- Potassium (K)
- Cesium (Cs)

### Step 2: Understand the Concept of Reducing Agents
A reducing agent is a substance that donates electrons to another substance, thereby reducing that substance while itself getting oxidized. The strength of a reducing agent depends on its ability to donate electrons.

### Step 3: Analyze the Atomic Radii of Alkali Metals
The atomic radii of alkali metals increase as we move down the group:
- Lithium (Li) < Sodium (Na) < Potassium (K) < Cesium (Cs)

### Step 4: Relate Atomic Radius to Reducing Strength
As the atomic radius increases, the effective nuclear charge experienced by the outermost electrons decreases. This means that the outermost electrons are held less tightly and can be donated more easily. Therefore:
- Cesium, with the largest atomic radius, is the strongest reducing agent.
- Lithium, with the smallest atomic radius, is expected to be the weakest reducing agent.

### Step 5: Consider Hydration Energy
However, hydration energy plays a crucial role in determining the reducing strength. Hydration energy is the energy released when ions are solvated by water. Lithium has a higher hydration energy compared to sodium. This means that while lithium is smaller and should be a weaker reductant, its higher hydration energy makes it less willing to donate electrons compared to sodium.

### Step 6: Conclusion
Based on the analysis:
- Sodium, despite being larger than lithium, has lower hydration energy, making it a weaker reducing agent than lithium.

Thus, the weak reductant among the alkali metals is **Sodium (Na)**.