Looks like no one added any tags here yet for you.
What does the conservation of mass state?
Atoms can’t be created or destroyed in a chemical reaction.
How are all the atoms rearranged into new substances?
All the atoms you had in the reactants must be present in the products.
What would you expect when it comes to measuring the mass of a reaction?
You would expect the mass at the start to be the same as the mass at the end.
What can happen to the mass sometimes?
Sometimes the mass can appear to change.