You are trapped on a desert island with plenty of water (both fresh and salt), a drinking glass, some wire, a radio, and no batteries. You do have a tin cup, a tube of toothpaste containing stannous fluoride (SnF₂, a source of Sn²⁺ ions), a silver pendant, and undeveloped black-and-white film (such film has silver bromide, AgBr, in it, a source of Ag⁺ ions).

(a) How would you use the above materials to construct a battery? Show how with a diagram, including an arrow over the wire to show which way the electrons flow. (You can make a salt bridge by soaking a sock in salt water and then dipping one end of the sock in one cell and the other end in the other cell.)

(b) Which metal would be eaten away? Explain.

(c) Which is the oxidizing agent?

(d) Which is the reducing agent?