Aluminothermy used for on the spot welding of large iron structures is based upon the fact that

Options

A. As compared to iron, aluminium has greater affinity for oxygen
B. As compared to aluminium, iron has greater affinity for oxygen
C. Reaction between aluminium and oxygen is endothermic
D. Reaction between iron oxide and aluminium is exothermic

Answer

To solve the question regarding aluminothermy used for on-the-spot welding of large iron structures, we need to analyze the options provided and understand the underlying chemical principles involved in the process.

### Step-by-Step Solution:

1. **Understand the Process of Aluminothermy**:
Aluminothermy is a process that involves the reaction of aluminum with metal oxides, particularly iron oxide (Fe2O3), to produce the metal and aluminum oxide (Al2O3). This reaction is highly exothermic, meaning it releases a significant amount of heat.

2. **Identify the Reaction**:
The relevant chemical reaction for aluminothermy can be written as:
\[ Fe2O3 + 2Al \rightarrow 2Fe + Al2O3 \]
In this reaction, aluminum reduces iron oxide to iron while itself being oxidized to aluminum oxide.

3. **Analyze the Affinity for Oxygen**:
- Aluminum has a greater affinity for oxygen compared to iron. This means that aluminum can effectively displace iron from its oxide due to its stronger tendency to bond with oxygen.
- Therefore, the first option states that "as compared to iron, aluminum has greater affinity for oxygen," which is true.

4. **Evaluate the Other Options**:
- **Option 2** states that "as compared to aluminum, iron has greater affinity for oxygen." This is incorrect because we established that aluminum has a greater affinity for oxygen.
- **Option 3** claims that "the reaction between aluminum and oxygen is endothermic." This is also incorrect; the reaction is exothermic.
- **Option 4** states that "the reaction between iron oxide and aluminum is exothermic." This is correct as the reaction releases heat.

5. **Conclusion**:
Based on the analysis, the correct options are:
- Option 1: As compared to iron, aluminum has greater affinity for oxygen.
- Option 4: The reaction between iron oxide and aluminum is exothermic.

### Final Answer:
The correct options are **Option 1 and Option 4**.

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