Which of the following gases is commonly used as a fuel to generate a high-temperature flame for producing light and for welding or cutting metals in oxy-fuel welding?

Introduction / Context:
Oxy-fuel welding and cutting processes rely on burning a fuel gas in oxygen to produce a very high-temperature flame capable of melting or cutting metals. Different fuel gases can be used, but one of the most common in traditional gas welding is acetylene. Understanding which compounds are gases used as fuels and which are liquids or solids used for other purposes helps in both chemistry and basic engineering questions. This question asks you to identify the gas used to generate light and to weld metals.

Given Data / Assumptions:

• The options are ethylene, acetylene, glycol, and oxalic acid.
• We are looking for a fuel gas suitable for generating a high-temperature flame.
• The flame should be suitable for both illumination (historically) and metal welding or cutting.
• We assume standard industrial and textbook descriptions of oxy-acetylene welding.

Concept / Approach:
Acetylene (C2H2) is a hydrocarbon gas that burns in oxygen to form a very hot flame, reaching temperatures high enough for welding and cutting steel. The oxy-acetylene flame can exceed 3000 degrees Celsius and has been widely used in metal fabrication. Ethylene (C2H4) is also a gas and burns with a flame, but it is not the standard gas for welding in basic exam questions. Glycol and oxalic acid are not gases; glycol is a liquid (for example, ethylene glycol used in antifreeze), and oxalic acid is a solid organic acid used in cleaning and bleaching. Therefore, acetylene is the fuel gas traditionally associated with high-temperature welding flames and “carbide lamps” used historically for light.

Step-by-Step Solution:
Step 1: Identify which substances are gases at room temperature. Ethylene and acetylene are gases; glycol is a liquid and oxalic acid is a solid. Step 2: Recall common welding gas names. The common gas used in traditional gas welding is acetylene in combination with oxygen (oxy-acetylene flame). Step 3: Consider historical use for light. Acetylene was also used in lamps (carbide lamps) for bright illumination in mines and bicycles. Step 4: Match this with the options and select “Acetylene”.

Verification / Alternative check:
Engineering and welding handbooks describe oxy-acetylene welding as one of the earliest and most widely used gas welding methods. The fuel gas is generated from acetylene cylinders or from reaction of calcium carbide with water. The high flame temperature and controllable flame characteristics make it suitable for welding and cutting. Ethylene is more commonly discussed in polymer chemistry as a monomer for polyethylene rather than as a primary welding gas. Glycol and oxalic acid are not fuel gases at all. This clear association between acetylene and welding confirms it as the correct answer.

Why Other Options Are Wrong:
Option A (Ethylene): Although it is a combustible gas, ethylene is not the classic welding gas referred to in basic exam questions; its main use is as a petrochemical feedstock. Option C (Glycol): Glycol is a liquid (for example, ethylene glycol) used as antifreeze and in plastics production, not as a welding gas. Option D (Oxalic acid): Oxalic acid is a solid organic acid used in cleaning and bleaching; it is not a fuel gas and cannot produce a welding flame.

Common Pitfalls:
Students may confuse ethylene and acetylene because their names sound similar and both are small hydrocarbons. Another mistake is not recognising that glycol and oxalic acid are not gases at room temperature. To avoid confusion, remember the phrase “oxy-acetylene welding”, which directly links acetylene with welding, and note that acetylene was also historically used in lamps to generate bright light.

Final Answer:
The gas used to generate light and to weld metals is Acetylene.