The statement that best justifies the conservation of mass during photosynthesis is:
The total number of carbon atoms on both sides is 6.
This statement highlights that the number of carbon atoms remains constant, and it reflects the principle of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction. For a complete justification, you could also argue that the total number of hydrogen and oxygen atoms is conserved, but this particular statement specifically addresses carbon, which is a key component of the reactants and products in this equation.