What is the main composition of thermite?

The primary composition of thermite is indeed iron(III) oxide, Fe2O3, combined with aluminum, which is represented by the choice that you selected.

This mixture is utilized in a highly exothermic reaction, specifically known as the thermite reaction. When aluminum powder is added to iron(III) oxide, it serves as a reducing agent and reacts with the metal oxide to produce elemental iron and aluminum oxide, along with a significant release of heat. The overall reaction can be summarized as follows:

Fe2O3 + 2Al → 2Fe + Al2O3 + heat

The high temperatures generated in this reaction can exceed 2500 degrees Celsius, making thermite particularly useful for applications such as welding railway tracks and in military applications for producing incendiary devices.

The other mixtures listed involve metals and metal oxides, but they do not produce the same intense reactions as the thermite reaction using iron(III) oxide and aluminum. Thus, the selection of Fe2O3 and Al captures the essence of thermite effectively.