Which of the following elements never show positive oxidation number?

Options

A. O
B. Fe
C. Ga
D. F

Answer

To solve the question "Which of the following elements never show positive oxidation number?" we will analyze each of the given options: Oxygen, Iron, Gallium, and Fluorine.

### Step-by-Step Solution:

1. **Understanding Oxidation States**:
- Oxidation states (or oxidation numbers) indicate the degree of oxidation of an atom in a compound. An oxidation state can be positive, negative, or zero.

2. **Analyzing Oxygen**:
- Oxygen typically has an oxidation state of -2 in most compounds (like H2O). However, it can also exhibit positive oxidation states, such as +1 in peroxides (e.g., H2O2) and +2 in compounds with fluorine (e.g., OF2).
- Therefore, oxygen can show positive oxidation states.

3. **Analyzing Iron**:
- Iron (Fe) can have multiple oxidation states, including +2 (ferrous) and +3 (ferric).
- Since iron can exhibit positive oxidation states, it is not the correct answer.

4. **Analyzing Gallium**:
- Gallium (Ga) can also exhibit positive oxidation states, primarily +1 and +3.
- Thus, gallium is not the correct answer either.

5. **Analyzing Fluorine**:
- Fluorine (F) is the most electronegative element and typically has an oxidation state of -1 in its compounds.
- Fluorine does not exhibit positive oxidation states because it always attracts electrons rather than losing them.
- Therefore, fluorine is the only element among the options that never shows a positive oxidation number.

6. **Conclusion**:
- Based on the analysis, the element that never shows a positive oxidation number is **Fluorine**.

### Final Answer:
- The correct answer is **Fluorine**.