An inorganic compound(A) made of two most occurring elements in the earth’s crust and used in building construction when made to react with carbon, forms a poisonous gas (B) which is most stable diatomic molecule. Compound (A) and (B) are

SiO2 is a compound of oxygen and silicon, the two most abundant elements of earth’s crust and is used in building construction.  (Poisonous gas and a stable diatomic molecule).SiO2+2C→ Si+2CO (Poisonous gas and a stable diatomic molecule).