Both helium (He) and magnesium (Mg) have two valence electrons. He represents a noble gas element, but Mg does not. Assign reason.

Explanation

To understand why helium (He) is a noble gas while magnesium (Mg) is not, despite both having two valence electrons, we can analyze their electronic configurations step by step.

### Step 1: Write the electronic configuration of Helium (He)
- Helium has an atomic number of 2, which means it has 2 electrons.
- The electronic configuration of helium is:
- K-shell: 2 electrons
- Therefore, the configuration can be written as: **1s²**

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