Despite the fact that aluminium is a reactive metal, it is a stable in air as well as in water. This is due to the formation of thin layer of oxide on the surface of aluminium metal which makes it passive for further attack. The layer is so useful, that in industry, it is purposely deposited by an electrolytic process called anodising. Reaction of aluminium with oxygen is highly exothermic and is called thermite reaction.
`2Al_((s)) +(3)/(2) O_(2(g)) rarr Al_(2)O_(3(s)) Delta_(f) H^(Ө) = -1670 kJmol^-1`
This reaction finds application for welding of metal and in the metallurgical extraction of many metals from their oxides.
The limitation is that to start the reaction, high temperature is required for which an ignition mixture is required.
The reaction which is not involved in thermite process is

Options

A. `2Fe + Al_(2)O_(3) rarr Fe_(2)O_(3) + 2Al`
B. `B_(2)O_(3) + 2Al rarr 2B + Al_(2) O_(3)`
C. `3Mn_(3) O_(4) + 8 Al rarr 9Mn + 4 Al_(2)O_(3)`
D. `Cr_(2)O_(3) + 2Al rarr 2Cr + Al_(2) O_(3)`

Explanation

To solve the question regarding the thermite process and identify which reaction is not involved in it, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Thermite Reaction**:
The thermite reaction is an exothermic reaction where aluminum powder is used to reduce metal oxides. The general form of the thermite reaction can be represented as:
\[ \text{Metal Oxide} + \text{Aluminum} \rightarrow \text{Metal} + \text{Aluminum Oxide} \]
Here, aluminum acts as a reducing agent.

2. **Identify the Given Reactions**:
We need to analyze the four reactions provided in the question. We will determine which one does not fit the thermite reaction criteria.

3. **Check Each Reaction**:
- **Reaction 1**: If it involves aluminum reducing a metal oxide, it is part of the thermite process.
- **Reaction 2**: Similarly, check if aluminum is used to reduce a metal oxide.
- **Reaction 3**: Again, verify if aluminum is reducing a metal oxide.
- **Reaction 4**: Check if this reaction involves aluminum reducing a metal oxide.

4. **Determine the Incorrect Reaction**:
After analyzing all four reactions, identify which one does not involve aluminum acting as a reducing agent for a metal oxide. This reaction will be the one not involved in the thermite process.

5. **Conclusion**:
Based on the analysis, the reaction that does not involve aluminum reducing a metal oxide is the answer to the question.

### Final Answer:
The reaction which is not involved in the thermite process is the one that does not include aluminum reducing a metal oxide.