Which of the following among alkali metal is most reactive ?

Options

A. Na
B. K
C. Rb
D. Cs

Answer

To determine which alkali metal is the most reactive, we can follow these steps:

### Step 1: Identify the Alkali Metals
The alkali metals in the periodic table include:
- Lithium (Li)
- Sodium (Na)
- Potassium (K)
- Rubidium (Rb)
- Cesium (Cs)

### Step 2: Understand the Reactivity Trend
The reactivity of alkali metals increases as you move down the group in the periodic table. This is due to the following reasons:
- **Atomic Size**: As you move down the group, the atomic size increases because additional electron shells are added.
- **Ionization Energy**: The ionization energy (the energy required to remove the outermost electron) decreases as the atomic size increases. This is because the outermost electron is farther from the nucleus and is less tightly held.

### Step 3: Compare the Alkali Metals
- **Lithium (Li)**: Smallest size, highest ionization energy.
- **Sodium (Na)**: Larger than Li, lower ionization energy than Li.
- **Potassium (K)**: Larger than Na, lower ionization energy than Na.
- **Rubidium (Rb)**: Larger than K, lower ionization energy than K.
- **Cesium (Cs)**: Largest size, lowest ionization energy among the alkali metals.

### Step 4: Conclusion
Since cesium (Cs) has the largest atomic size and the lowest ionization energy among the alkali metals, it is the most reactive alkali metal.

### Final Answer
The most reactive alkali metal is **Cesium (Cs)**.

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