When a molecule is reduced, it always :

Options

A. gains a proton
B. gains an electron
C. loses a proton
D. loses an electron

Explanation

To solve the question "When a molecule is reduced, it always:", we need to understand the concept of reduction in chemistry, particularly in the context of redox (reduction-oxidation) reactions.

### Step-by-Step Solution:

1. **Understanding Reduction**:
- Reduction is a chemical process where a molecule gains electrons. This is a fundamental concept in redox reactions, where one species is oxidized (loses electrons) and another is reduced (gains electrons).

2. **Identifying the Options**:
- The question provides four options:
a) Gain a proton
b) Gain an electron
c) Loss of a proton
d) Loss of an electron

3. **Evaluating Each Option**:
- **Gain a proton**: This is incorrect. Gaining a proton does not define reduction.
- **Gain an electron**: This is correct. Gaining electrons is the hallmark of reduction.
- **Loss of a proton**: This is incorrect. Losing a proton does not indicate reduction.
- **Loss of an electron**: This is incorrect. Losing electrons is associated with oxidation, not reduction.

4. **Conclusion**:
- Based on the definitions and evaluations, when a molecule is reduced, it always gains an electron.

### Final Answer:
When a molecule is reduced, it always **gains an electron**.

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