Aflashbulb contains magnesium and oxygen before use and magnesium oxide afterward, but its mass does not change.

This is an example of law of conservation of mass, which states that the total quantity of mass doesn't change means, in an isolated system mass is neither created nor destroyed by any chemical reactions or physical transformations.

According to law of mass conservation in a chemical reaction:

Mas of the Products = Mass of the Reactants

Engineers have contribute to society in many ways like making the technology we use today or any type of power energy material

It is a product