The composition of the thermite mixture is:

A pyrotechnic combination of metal powder fuel and metal oxide is known as thermite. Due to its high boiling point and inexpensive price, aluminium is one of its many components. Iron (III) oxide is one of the oxidizers. Thermite welding, which is frequently used to link rail tracks, metal refining, weaponry, fireworks, etc., all use this mixture.

Thermite is a mixture of oxide of one metal and powder of another metal. Aluminium is often used as a metal to reduce metal oxide. Aluminium is common due to its high boiling point and low cost.
e.g. iron thermite (${\mathrm{Fe}}_2{\mathrm{O}}_3 + \mathrm{Al}$), chromium thermite (${\mathrm{Cr}}_2{\mathrm{O}}_3 + \mathrm{Al}$), copper thermite     ($\mathrm{CuO} + \mathrm{Al}$).
Explanation of example (${\mathrm{Fe}}_2{\mathrm{O}}_3 + \mathrm{Al}$) Aluminium and iron oxides, where aluminium acts as a reducing agent. Your metal oxide is iron oxide. During the reaction, a large amount of energy is released. This heat (energy) is so intense that thermite reactions can be used to heat other metals together.
${\mathrm{Fe}}_2{\mathrm{O}}_3 + 2\mathrm{Al} \to {\mathrm{Al}}_2{\mathrm{O}}_3+ 2\mathrm{Fe} + \mathrm{heat}$
The thermite contains a mass ratio of ferric oxide (Iron (III) oxide) and aluminium of 3:1.

Hence, the correct option is B.