Final answer:
Without more context on the substrate and reaction conditions, it's not possible to accurately predict the exact mono-substitution bromination product, even when employing knowledge of chemical reactivity and atomic economy.
Step-by-step explanation:
To predict the major mono-substitation product for a reaction involving bromine (Br2) and iron (Fe) in the presence of iron(II) bromide (FeBr2), we need to use our knowledge of chemical reactivity and the principle of atomic economy. In a bromination reaction, Fe would likely act as a catalyst in the formation of organobromine compounds.
The information provided is not sufficient to predict the exact substrate that is being brominated, but generally, one can expect that the reaction will lead to an addition of a bromine atom to the most reactive position of an unsaturated organic compound (like an alkene or an aromatic ring) present in the system. However, without additional information about the substrate and reaction conditions, we cannot determine the exact product.