E. A chemical reaction took place. It's probable that the stains in the silver plate were the result of the reaction between the sulfur in the air and the silver of the platter. They produced silver sulfide. By placing the stained silver platter with the aluminum foil in a container with hot water and baking soda, we reverse that initial reaction. We produced aluminum sulfide (that becomes part of the solution of water) and the silver was free and clean.
3 Ag₂S + 2 Al ---> 6 Ag + Al₂S
silver sulfide + aluminum ----> silver + aluminum sulfide
F. The law of conservation of mass states that mass in an isolated system is neither created nor destroyed by chemical reactions. In a reaction the atoms join together in different ways to form different products. In a balanced reaction we have the same number of atoms of each element on both sides of the equation.
For example in the equation of our reaction:
3 Ag₂S + 2 Al ---> 6 Ag + Al₂S
We have 6 atoms of Ag, 3 atoms of S and 2 atoms of Al on both sides of the equation. They just combined in a different way to produce different compounds. But no mass was created or destroyed.