This element is the most widespread catalyst of the azide-alkyne cycloaddition. Salts of this element catalyze the reaction of diazonium salts into aryl halides in the Sandmeyer reaction. A brick-red 
This element is the most widespread catalyst of the azide-alkyne cycloaddition. Salts of this element catalyze the reaction of diazonium salts into aryl halides in the Sandmeyer reaction. A brick-red oxide of this element is created as a precipitate to indicate the presence of reducing sugars in Benedict’s test. This element, which produces a blue-green color in a flame test, forms the green surface layer verdigris when exposed to air for long periods of time. For 10 points, name this element that, with tin, forms the alloy bronze.