Which of the following has zero valency

Options

A. Sodium
B. Beryllium
C. Aluminium
D. Krypton

Answer

To determine which of the given options has zero valency, we need to understand the concept of valency and how it relates to the electron configuration of elements.

### Step-by-Step Solution:

1. **Understanding Zero Valency**:
- Zero valency means that the outermost shell of an atom is completely filled with electrons. This typically occurs in noble gases, which have stable electron configurations.

2. **Identifying Noble Gases**:
- Noble gases are elements found in Group 18 of the periodic table. They include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). All these gases have a complete outer electron shell.

3. **Analyzing the Options**:
- We need to analyze the electron configurations of the given elements to see which one has a completely filled outer shell.
- **Sodium (Na)**: Atomic number 11, electron configuration: 1s² 2s² 2p⁶ 3s¹. The outer shell (3s) is not filled.
- **Beryllium (Be)**: Atomic number 4, electron configuration: 1s² 2s². The outer shell (2s) is filled, but the 2p is empty, so it does not have zero valency.
- **Aluminium (Al)**: Atomic number 13, electron configuration: 1s² 2s² 2p⁶ 3s² 3p¹. The outer shell is not completely filled.
- **Krypton (Kr)**: Atomic number 36, electron configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 4p⁶. The outer shell (4s and 4p) is completely filled.

4. **Conclusion**:
- Among the options analyzed, krypton (Kr) is the only element that has a completely filled outer shell, thus it has zero valency.

### Final Answer:
- The element with zero valency is **Krypton (Kr)**.

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