According to classical concept, oxidation involves

Options

A. Addition of oxygen
B. Addition of electronegative element
C. Removal of either hydrogen or some electropositive element
D. All of these

Answer

### Step-by-Step Solution:

1. **Understanding Oxidation**: According to the classical concept, oxidation is defined primarily in two ways:
- The addition of oxygen to a substance.
- The removal of hydrogen or any electropositive element from a substance.

2. **Addition of Oxygen**:
- When oxygen is added to a compound, it is considered oxidation.
- **Example**: When hydrogen reacts with copper oxide (CuO), it produces copper (Cu) and water (H2O).
- Reaction: \( \text{CuO} + \text{H}_2 \rightarrow \text{Cu} + \text{H}_2\text{O} \)
- Here, the addition of oxygen to hydrogen results in the formation of water, indicating that oxidation has occurred.

3. **Addition of Electronegative Elements**:
- Oxidation can also occur through the addition of any electronegative element.
- **Example**: When chlorine is added to hydrogen sulfide (H2S), it forms hydrochloric acid (HCl) and sulfur (S).
- Reaction: \( \text{H}_2\text{S} + \text{Cl}_2 \rightarrow \text{2HCl} + \text{S} \)
- The addition of chlorine (an electronegative element) leads to the oxidation of hydrogen sulfide.

4. **Removal of Hydrogen or Electropositive Elements**:
- The removal of hydrogen or any electropositive element is also classified as oxidation.
- In the previous example, when chlorine is added to H2S, sulfur is removed, which is also indicative of oxidation.

5. **Conclusion**:
- Based on the definitions and examples provided, we can conclude that:
- 1) Addition of oxygen is oxidation.
- 2) Addition of any electronegative element is oxidation.
- 3) Removal of hydrogen or any electropositive element is also oxidation.
- Therefore, the correct answer is that all of these options describe oxidation according to the classical concept.

### Final Answer:
**All of these (Option 4)**.

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