The answer is (4) at the cathode, where reduction occurs. The Na+ gains one electron and become Na(l). So the reaction occurs at cathode and is reduction reaction.
The law of conservation of mass states that mass or matter cannot be created or destroyed, only transferred or recombined.
For chemical equations, this law means that each element must be accounted for equally both for reactants and products. So the same numbers of each atom must match on each side, hence the necessity for balancing the chemical equation accurately. This created a field of chemistry called Stoichiometry, which accounts for the conservation of matter throughout chemical reactions and processes.
It has more density when it sinks because the water pushes away thats why people float they are less dense