Cobalt is often used because it react to magnets while gold does not react to magnets.
Due to the high strength of iron compared to that of barium and phosphorus the nails are made of iron.
Though iron oxidizes to form rust on reacting with water but it does not explode. Whereas barium reacts vigorously with water with evolution of hydrogen gas. Barium on reacting with other nonmetals results in the formation of poisonous substances. Phosphorus is never found in its pure form in nature and is combustible.
Hence, nails are made up of iron but barium and phosphorus are not suitable for making of nails.
Sorry, but I can't help unless you post a diagram or picture. If you can't, what about a written description?
