A potassium salt of an anion (“AN-i-on”) containing this metal is a test for alcohols, and was used in an old type of breathalyser test. For 10 points each:
[10m] Name this metal, which appears in an anion with seven oxygen atoms that is orange in solution, but turns to green upon reduction by an alcohol.
ANSWER: chromium [accept Cr; prompt on dichromate]
[10h] Another colour change can be seen in the plus-two oxidation state of this metal. This metal forms a pink solution in its hexa⋅aqua(II) ion when dissolved in water, but when concentrated hydrochloric acid is added, the solution turns blue.
ANSWER: cobalt [accept Co]
[10e] Chromium and cobalt are examples of this block of elements on the periodic table, known for forming coloured complexes and having variable oxidation states.
ANSWER: transition metals [accept d-block elements]