Hello! I’m having a tough time grasping the concept of this and here’s the specific question I’m doing it says

In a chemical reaction:

A- there is always emission of energy in the form of heat

B- the total mass of the products is not necessarily equal to the total mass of the reactants

C- the total number of product molecules must be equal to the total number of reactant molecules

D- the total mass of the product is always equal to the total mass of the reactants

E - you can have transformation of one element into another

The answer is D. But, I can’t quite understand it because I fail to wrap my head around the mass of the reactants ALWAYS being equal to the mass of the products. I personally picked B. I put it into chatGPT and it said this was the law of conservation of mass in a CLOSED SYSTEM which does make sense but I feel like the question is a bit too vague? please give me your input and thanks for reading