From hydrogen, sodium, zinc and argon select
Least reactive element.

Explanation

To determine the least reactive element among hydrogen, sodium, zinc, and argon, we can analyze the reactivity of each element based on their properties.

### Step-by-Step Solution:

1. **Identify the Elements**: We have four elements: Hydrogen (H), Sodium (Na), Zinc (Zn), and Argon (Ar).

2. **Classify the Elements**:
- **Hydrogen**: A non-metal and a reactive gas.
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