A Reaction Vessel Contains Equal Masses of Iron and Oxygen

Multiple Choice

A reaction vessel contains equal masses of iron and oxygen. How much FeO could theoretically be produced?

A) an amount equal to the sum of the masses of iron and oxygen
B) an amount greater than the sum of the masses of iron and oxygen
C) an amount less than the sum of the masses of iron and oxygen
D) There is no way to tell.
E) It depends on the reaction conditions.