The group in the modern periode table, in which all the elements do not have same number of electrons in their valence shell is :

Options

A. `13^(th)`
B. `11^(th)`
C. `9^(th)`
D. `18^(th)`

Explanation

To solve the question, we need to identify the group in the modern periodic table where the elements do not have the same number of electrons in their valence shell. Here’s a step-by-step breakdown of the solution:

### Step 1: Identify the Groups in the Periodic Table
The periodic table is organized into groups (columns) and periods (rows). Each group contains elements with similar properties.

### Step 2: Focus on Group 18 (Noble Gases)
Group 18, also known as the noble gases, includes the elements helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn).

### Step 3: Examine the Electron Configurations
Let's look at the electron configurations of the noble gases:
- **Helium (He)**: 1s² (2 electrons in the valence shell)
- **Neon (Ne)**: 1s² 2s² 2p⁶ (8 electrons in the valence shell)
- **Argon (Ar)**: 1s² 2s² 2p⁶ 3s² 3p⁶ (8 electrons in the valence shell)
- **Krypton (Kr)**: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 4p⁶ (8 electrons in the valence shell)
- **Xenon (Xe)**: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 4p⁶ 5s² 5p⁶ (8 electrons in the valence shell)
- **Radon (Rn)**: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 4p⁶ 5s² 5p⁶ 6s² 6p⁶ (8 electrons in the valence shell)

### Step 4: Analyze the Valence Electrons
From the configurations, we can see that:
- Helium has 2 electrons in its valence shell.
- All other noble gases (Ne, Ar, Kr, Xe, Rn) have 8 electrons in their valence shells.

### Step 5: Conclusion
Since helium is the only element in Group 18 that does not have 8 electrons in its valence shell (it has 2), we conclude that Group 18 is the group where not all elements have the same number of valence electrons.

### Final Answer
The group in the modern periodic table, in which all the elements do not have the same number of electrons in their valence shell, is **Group 18 (Noble Gases)**.

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