When the reaction goes into completion, they will produce 2.5g. This is complement the law of conservation of mass.
According to the law of conservation of mass "in a chemical reaction, matter is neither created nor destroyed but transformed from one form to another".
The mass of reactants and products in a chemical reaction must be the same.
There is no change in mass in moving from reactant to product
So, if we start with 2.5g of reactants, we must end with 2.5g of products.
