Which candle burned the longest time why

May someone me with these science questions

What is a substance? a. a physical property of matter b. a chemical property of matter c. an element or compound that cannot be physically separated d. characteristics used to tell the difference between mixtures

Achemical reaction is done in the setup shown , resulting in a change of mass. what will happen if the same reaction is done in a sealed container that is placed on the electronic balance?