If a chemical reaction such as photosynthesis begins with 6 atoms of carbon c , how many atoms of carbon c should be in the products?
a. 12 atoms of carbon c
b. 6 atoms of carbon c
c. 3 atoms of carbon c
d. 2 atoms of carbon c

B. 6 atoms of carbon C
I would think this is the answer, because one can't just delete or add atoms; otherwise, the equation would be unbalanced. This also abides with the Law of Conservation of Mass.

Plus, I also came to that conclusion because if we look at the net equation of photosynthesis:
––> 
The number of Carbon atoms is 6 on both the reagent's side and the product's side.