In the manufacture of iron, the principal reaction in the zone of heat absorption of the blast furnace is

Question

$ (a)\;CO_2(g)+C(s) \longrightarrow 2CO(g) \\(b)\;2C+ O_2(g) \longrightarrow 2CO_2(g) \\(c)\;3C+O_2 \longrightarrow C_3O_2 \\ (d)\;2C+O_2 \longrightarrow 2CO $