Consider the following separations of materials. State whether a physical process or a chemical reaction is involved in each separation.
a. Sodium chloride is obtained from seawater by evaporation of the water.
b. Mercury is obtained by heating the substance mercury(II) oxide; oxygen is also obtained.
c. Pure water is obtained from ocean water by evaporating the water, then condensing it.
d. Iron is produced from an iron ore that contains the substance iron(III) oxide.
e. Gold is obtained from river sand by panning (allowing the heavy metal to settle in flowing water).