Under standard conditions, which of the following operations results in a spontaneous chemical reaction taking place? a. A piece of aluminum metal is placed in an aqueous solution of potassium nitrate. b. Iodine crystals are added to an aqueous solution of sodium chloride. c. A piece of silver metal is placed in an aqueous solutions of copper(II) nitrate. d. Chlorine gas is bubbled through an aqueous solution of sodium bromide. e. At least two of the above (A-D) result in a spontaneous chemical reaction