Correct Answer - C
About 5 mg Cu are required in the daily human diet. A deficiency of this element renders the body unable to use Fe stored in the liver. There are numberous Cu proteins throughout the living world, the most intriguing being the hemocyanins. These moleculs are common oxygen carriers in the invertebrate world: Crabs, lobsters, octopi, scorpions and snail all have bright blue blood. At the same time, an excess of Cu is highly poisonouus, particularly to fish. This is why Cu coins should never be thrown into fish pools for 'good luck'. Humans usually excrete any excess, but a biochemical (genetic) defect can result in Cu accumulation in the liver, kidneys, and administering chelating agents, which complex the metal ion and allow it to be excreted harmlessly. The reactivity decreases down the group 11 and in its intertness gold resembles Pt metals. The best known oxidation states in aqueous solution are`+2` for Cu, `+1` for Ag and `+3` for Au. This agrees their ionization enthalpies, As has the lowest first ionization enthalpy, the sum of the first and second is lowest for Cu and the sum of the first, second and third is the lowest for Au. However, the elements are not well-related in their chemical behaviour, 'Horizonatal' similarities with their neighbours in the periodic table are in fact more noticeable than vertical ones.
