Aluminium is used __________ because it reacts with oxygen and nitrogen.

Aluminium (Al) is a highly reactive metal that forms a protective oxide layer under normal conditions. Its chemical reactivity with oxygen and nitrogen makes it useful in metallurgical processes, particularly for purifying molten metals. When metals like iron, copper, or steel are melted, dissolved oxygen and nitrogen can create defects such as blowholes or porosity in the solidified metal.

Adding small amounts of aluminium to the molten metal causes it to react with oxygen and nitrogen:

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  With oxygen: 4Al + 3O₂ → 2Al₂O₃

  
  


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  With nitrogen: 2Al + N₂ → 2AlN

  
  

The reactions produce aluminium oxide (Al₂O₃) and aluminium nitride (AlN), which are insoluble in the molten metal. These compounds attach to air bubbles and float to the surface, effectively removing dissolved gases and preventing defects in the solidified metal.

This process is widely used in steel and non-ferrous metallurgy as a deoxidizer and denitrifier, improving the strength, ductility, and surface finish of the final product. The technique is sometimes referred to as alloy deoxidation or air purification of molten metal.

Aluminium’s ability to react with both oxygen and nitrogen is crucial here. Other uses of aluminium, such as making alloys or acting as an insulator, are unrelated to its reactivity with gases. Its role as a nitrometer is specific to laboratory gas measurement, which is different from industrial purification.

Therefore, the correct application based on its chemical behavior is: to remove air bubbles from molten metal. This highlights aluminium’s importance in practical inorganic chemistry and metallurgy, where understanding its reactivity ensures high-quality metal production