………is the lightest mixture.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for the lightest mixture. However, it seems to be a misunderstanding, as the term "lightest mixture" is not commonly used in chemistry.

2. **Identifying the Lightest Element**: Instead of a mixture, we should focus on identifying the lightest element in the periodic table.

3. **Researching Elements**: The periodic table lists all known elements, and we need to find the one with the lowest atomic number, which indicates its lightness.

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