Answer: The atoms present at the beginning of the reaction is equal to the atoms present at the end of the reaction.
The reason for this is because matter can neither be created nor be destroyed in an ordinary chemical reaction.
Explanation: During photosynthesis, six molecules of water reacts with six molecules of carbon dioxide to form one molecule of glucose and six molecules of oxygen. The equation for the reaction is 6CO2 + 6H2O --> C6H12O6 + 6O2
At the beginning of the reaction, there is 6 carbon atoms, 18 oxygen atoms and 12 hydrogen atoms while at the end of the reaction, there is 6 carbon atoms, 12 hydrogen atoms and 18 oxygen atoms.
The reason for this is because according to the law of conservation of mass, matter can neither be created be created nor be destroyed in an ordinary chemical reaction. There the number of atoms present at the beginning of the reaction must be equal to the number of atoms present at the end of the reaction.
