In gas welding, especially oxy acetylene welding, which combination of gases is commonly used together as the fuel and the oxidizing gas?

Introduction / Context:
Gas welding is a common method used in metal fabrication and repair. The best known type is oxy acetylene welding, which relies on a mixture of gases to produce a very hot flame capable of melting and joining metals. Understanding which gases are used as the fuel and oxidizing components is basic knowledge in welding technology and general science examinations. This question asks which combination of gases is used in such welding processes.

Given Data / Assumptions:

• The welding process referred to is oxy acetylene or similar gas welding.
• Typical setups use a separate fuel gas cylinder and an oxidizing gas cylinder.
• The options list acetylene alone, oxygen alone, oxygen and acetylene together, and nitrogen with other gases.
• The goal is to identify the correct combination for producing a hot welding flame.

Concept / Approach:
In oxy acetylene welding, acetylene (C2H2) is used as the fuel gas and oxygen (O2) as the oxidizing gas. When acetylene is burned in pure oxygen rather than in air, the flame temperature is much higher, reaching around 3000 °C, which is sufficient to melt steel and many other metals. Using acetylene alone with air does not produce a flame as hot or as suitable for high quality welding. Oxygen alone does not burn; it supports combustion of fuels. Nitrogen is relatively inert and is not used as a fuel or oxidizer in standard welding flames. Therefore, the correct combination is oxygen and acetylene together.

Step-by-Step Solution:
Step 1: Identify acetylene (C2H2) as a common fuel gas used in industrial cutting and welding because it burns with a very hot flame. Step 2: Recognise that oxygen is needed as the oxidizing gas to support combustion of acetylene and raise the flame temperature. Step 3: Recall that the term oxy acetylene welding itself indicates the use of both oxygen and acetylene. Step 4: Note that acetylene alone or oxygen alone cannot provide the ideal welding flame: fuel alone cannot burn without oxidizer, and oxygen requires a fuel. Step 5: Conclude that the combination of oxygen and acetylene is the correct answer and select that option.

Verification / Alternative check:
Training manuals and engineering references describe oxy fuel welding as a process that uses a fuel gas, such as acetylene, and oxygen. The specific name oxy acetylene welding arises from the pairing of these two gases. Nitrogen is not part of the standard gas pair, and other fuel gases like propane or hydrogen may be used in different applications but are not mentioned in this particular question. This consistent description across practical and theoretical resources confirms that oxygen and acetylene are indeed the gases used together in the common welding process referred to here.

Why Other Options Are Wrong:
Acetylene alone cannot produce a proper welding flame without an adequate oxidizing gas; with air, the flame is cooler and less suitable for precision welding. Oxygen alone is not a fuel and cannot burn by itself; it only supports combustion of other substances. The combination of nitrogen, oxygen, and acetylene is not standard for gas welding, and nitrogen, being relatively inert, would mostly dilute the flame rather than enhance it. Therefore, none of these alternatives correctly represent the standard gas combination for oxy acetylene welding.

Common Pitfalls:
One common error is to focus only on the fuel gas acetylene and forget that an oxidizer is always needed for combustion. Another pitfall is confusing atmospheric air, which contains nitrogen and oxygen, with the pure oxygen used in welding. Students might think that because air contains nitrogen, nitrogen must also be part of the welding gas mixture. To avoid this confusion, remember that welding sets use separate cylinders: one for the pure fuel gas (such as acetylene) and one for pure oxygen, which are mixed in the torch to produce a high temperature flame.

Final Answer:
Gas welding, especially oxy acetylene welding, commonly uses a combination of oxygen and acetylene as the oxidizing gas and fuel gas, respectively.