This is the heaviest element in a solution added to test for the presence of phenols. Its chloride, 
This is the heaviest element in a solution added to test for the presence of phenols. Its chloride, though milder than aluminum chloride, is still widely used as a Lewis acid in Friedel-Crafts reactions. Its pentacarbonyl is commonly seen because this element has eight valence electrons. Mossbauer spectroscopy is commonly performed using an isotope of this element. The most famous sandwich compound consists of this metal bound to two cyclopentadienyl rings. This metal and cyanide are present in Prussian blue, and its sulfide is known as pyrite, or Fool's Gold. For 10 points, name this transition metal which is oxidized from +2 to +3 during rusting.
This is the heaviest element in a solution added to test for the presence of phenols.
iron [or Fe; or ferrum]