To weld metals together, high temperature is required. Such a high temperature is obtained by burning :

Options

A. Acetylene in oxygen
B. LPG in oxygen
C. Methane in oxygen
D. Acetylene in nitrogen

Explanation

To solve the question, "To weld metals together, high temperature is required. Such a high temperature is obtained by burning:", we need to analyze the options provided and determine which fuel produces the highest temperature when burned.

### Step-by-Step Solution:

1. **Understanding the Requirement**:
- Welding requires high temperatures to melt and fuse metals together.

2. **Analyzing the Options**:
- We need to look at the combustion of different fuels to see which one produces the highest temperature.

3. **Option 1: Acetylene in Oxygen (C2H2 + O2)**:
- Acetylene (C2H2) is known for its high flame temperature when burned in oxygen. The reaction produces a lot of energy due to the presence of a triple bond between carbon atoms, which releases significant energy upon combustion.
- This is commonly used in welding processes, such as oxy-acetylene welding, because it can reach temperatures around 3,500°C.

4. **Option 2: LPG in Oxygen**:
- Liquefied Petroleum Gas (LPG) can also burn in oxygen, but it does not reach the same high temperatures as acetylene. It is primarily used for heating and cooking.

5. **Option 3: Methane in Oxygen**:
- Methane (CH4) burns in oxygen but produces a lower flame temperature compared to acetylene. It is often used for heating but is not suitable for welding due to insufficient temperature.

6. **Option 4: Acetylene in Nitrogen**:
- Nitrogen does not support combustion, so burning acetylene in nitrogen will not produce any flame or high temperature.

7. **Conclusion**:
- After analyzing all options, it is clear that the highest temperature for welding is obtained by burning acetylene in oxygen. Therefore, the correct answer is **Option 1: Acetylene in Oxygen**.

### Final Answer:
**Acetylene in Oxygen (C2H2 + O2)** produces the high temperature required for welding metals.

---