Most inert among the following 

Options

A. He
B. Ne
C. Ar
D. Kr

Answer

To determine which of the given noble gases is the most inert, we can analyze the properties of each gas: helium, neon, argon, and krypton.

### Step-by-Step Solution:

1. **Identify the Noble Gases**: The noble gases in question are helium (He), neon (Ne), argon (Ar), and krypton (Kr). These gases belong to Group 18 of the periodic table.

2. **Understand the Electron Configuration**:
- Helium has the electron configuration of 1s².
- Neon has the electron configuration of [He] 2s² 2p⁶.
- Argon has the electron configuration of [Ne] 3s² 3p⁶.
- Krypton has the electron configuration of [Ar] 4s² 4p⁶.
All these gases have a complete outer shell of electrons, which contributes to their inertness.

3. **Consider Ionization Energy**:
- Ionization energy is the energy required to remove an electron from an atom. The higher the ionization energy, the more difficult it is to remove an electron, and thus the more inert the gas is.
- Helium has the highest ionization energy among the noble gases due to its small atomic size and full outer shell.

4. **Compare Sizes**:
- Helium is the smallest noble gas, which results in a higher effective nuclear charge experienced by its electrons. This leads to a stronger hold on the electrons, making it less likely to participate in chemical reactions.

5. **Conclusion**:
- Since helium has the highest ionization energy and is the smallest noble gas, it is the most inert among the options provided. Therefore, the answer is **helium (He)**.

### Final Answer:
The most inert among the following gases is **helium (He)**.

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