To weld metals together, a high temperature is required. This high temperature is obtained by burning a fuel gas in the presence of oxygen. The correct answer is option 1, acetylene in oxygen.

Option 1: Acetylene in oxygen - Acetylene is a commonly used fuel gas in welding. When acetylene is burned in the presence of oxygen, it produces a high temperature flame that can reach up to 6,000 degrees Fahrenheit. This flame is ideal for melting and joining metals together during welding processes.

Option 2: LPG in oxygen - LPG (liquefied petroleum gas) is primarily composed of propane and butane. While LPG can be used as a fuel for cutting metals, it is not typically used as a primary fuel for welding. LPG typically burns at a lower temperature compared to acetylene.

Option 3: Methane in oxygen - Methane gas, commonly known as natural gas, is not commonly used as a fuel for welding. Methane burns at a lower temperature compared to acetylene and may not provide the high temperature required for welding.

Option 4: Acetylene in nitrogen - Mixing acetylene with nitrogen is not a typical practice for welding. Nitrogen does not contribute to the