Why might the percent yield of copper produced be less than 100% of the expected amount?

[ ] There are impurities in the substances.
[ ] The reaction might not have gone to completion.
[ ] The amount of one of the reactants might be measured incorrectly.

(you can pick multiple)

The reasons can be :

There are impurities in substances

adding or remove a gaseous reactant or product changes the concentrations. if the concentration of reactant or product is increased, the system will shift away from the side in which concentration was increased (i.e. if the concentration of reactants is increased, the system will shift toward the products. if more products are added, the system will shift to form more reactants). conversely, if the concentration of reactant or product is decreased, the system will shift toward the side in which concentration was decreased (i.e. if reactants are removed, the system will shift to form more reactants. if the concentration of products is decreased, the equilibrium will shift toward the products).

explanation:

i believe the answer is true.