Question

In the thermite process reducing agent used is:
A. C
B. CO
C. Al
D. None of these

Answer 1

Hint: As the name suggests, thermite is pyrotechnic which is a composition of metal powder and metal oxides and when it is ignited by heat, it will undergo exothermic reduction-oxidation which is a redox reaction.

Complete step-by-step answer:
As we know thermite process is a process in which reducing metallic oxides by using finely divided aluminium powder and when the mixture of aluminium and the oxide is ignited it causing the aluminium to be oxidized and the metal oxide to be reduced to the metal.
Among various diverse compositions of thermites, fuels include aluminium, zinc, magnesium, titanium, silicon, and boron. Among these, aluminium is common because of its high boiling point and low cost.
Now let us see, in the given example, elemental aluminium reduces the oxide of another metal, common example iron oxide and this is because of aluminium forms stronger and more stable bonds with oxygen than iron:
\[F{{e}_{2}}{{O}_{3}}+2Al\to 2Fe+A{{l}_{2}}{{O}_{3}}\]
Aluminium oxide and elemental iron are products with a large amount of heat. In this reaction, reactants are powdered and mixed with a binder to prevent separation by keeping material solid.
Apart from these other metals oxides can also be used for example chromium oxide which is used to generate the given metal in its elemental form.
Similarly, copper thermite reaction using copper oxide and elemental aluminium which can be used for creating electric joints in a process termed as cad welding which produces elemental copper in following chemical equation:
\[3CuO+2Al\to 3Cu+A{{l}_{2}}{{O}_{3}}\]
Now, from the above it is concluded that the correct option is (C).
Let us see why the other options are incorrect:
As we know, aluminium powder and iron oxide used in thermite reaction in which iron oxide loses oxygen to form iron and hence iron oxide are reduced whereas, in the case of Carbon as reducing agent in thermite reaction, it gains oxygen to form carbon dioxide and therefore carbon is oxidized and hence is not used as reducing agent.
Similarly, for Carbon Monoxide, which is a strong reducing agent, it reduces the oxides of less active metals to their respective metals and itself gets oxidized to carbon dioxide in the process.

Additional information:
All the above reactions are also called the Goldschmidt process which is used for thermite welding and frequently used to join railway tracks, Thermites have also been used in metal refining, incendiary weapons, and in disabling munitions.

Note: Don’t confuse Carbon and Carbon monoxide with aluminium as a reducing agent because these two itself get oxidized to form carbon dioxide and hence not used as a reducing agent.