Hydrogen gas is ____ to litmus.

Explanation

**Step-by-Step Solution:**

1. **Understanding Litmus:** Litmus is a natural dye that is used as an indicator to determine whether a substance is acidic or basic. It changes color depending on the pH of the solution it is in contact with.

2. **Identifying Hydrogen Gas:** Hydrogen gas (H₂) is a diatomic molecule and is known to be a neutral gas. It does not possess acidic or basic properties.

3. **Neutral Nature of Hydrogen:** Since hydrogen gas is neither acidic nor basic, it does not affect the pH of a solution. Therefore, it does not change the color of litmus paper.

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