Hydrogen is a _____ `("reducing"//"oxidising")` agent.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Terms:**
- First, we need to understand what a reducing agent and an oxidizing agent are.
- A reducing agent is a substance that reduces another substance by donating electrons or hydrogen, or by removing oxygen from it.

2. **Definition of Reduction:**
- Reduction is defined as the gain of electrons or hydrogen, or the loss of oxygen.
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