Which one of the following atoms will have the smallest size ?

Options

A. Mg
B. Na
C. Be
D. Li

Explanation

To determine which atom has the smallest size among the given options, we can follow these steps:

### Step 1: Understand Atomic Size
Atomic size generally refers to the radius of an atom, which can be influenced by the number of electron shells and the effective nuclear charge experienced by the outermost electrons.

### Step 2: Identify the Group of Elements
The question mentions s-block elements, which include the alkali metals (Group 1) and alkaline earth metals (Group 2). The elements in these groups are characterized by their outermost electrons being in the s orbital.

### Step 3: List the Elements
From the video transcript, the following elements are mentioned:
- Alkali Metals: Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs)
- Alkaline Earth Metals: Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba)

### Step 4: Compare Atomic Sizes
- Atomic size increases down a group due to the addition of electron shells.
- Among the alkali metals, Cesium (Cs) is the largest, while Lithium (Li) is the smallest.
- Among the alkaline earth metals, Barium (Ba) is the largest, while Beryllium (Be) is the smallest.

### Step 5: Conclusion
Since Beryllium (Be) is the smallest atom among the listed s-block elements, the answer to the question is:
**Beryllium (Be) has the smallest size among the given options.**

### Final Answer
The atom with the smallest size is **Beryllium (Be)**.

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