Does the production of a new gas by a substance represent a chemical property. explain?

Silver tarnishes as silver metal reacts with hydrogen sulfide, h2s, in the air. in this reaction, dark silver sulfide, au2s, covers the surface of silver. when silver is polished, this coating of silver sulfide can be removed from the surface. this makes the silver shiny again. enter the coefficients that balance the tarnishing reaction equation. (type 1 for no coefficient.)

Calculate the number of molecules present in 0.750 mol of mgo.

Which factor is likely to impact the possible number of compounds ?