Water-soluble complexes of nickel in this oxidation state can be prepared with TPPTS. Gold atoms with this oxidation state are attached to cyclic alkyl amino carbenes in complexes isolated by (-5[1])Guy Bertrand’s lab. A form of iron in this oxidation state is used to construct permeable reaction barriers used for groundwater remediation. (-5[1])Nickel in this oxidation state is often sourced from a complex in which it is attached to two (*) 1,5-cyclo·octa·dienes. Before the oxidative addition step, (10[1])this is the oxidation state of palladium (10[1])in the catalyst (10[1])of the (10[1])Heck reaction and most other palladium-catalyzed cross-couplings. (-5[1])A half-reaction that produces an element in this oxidation state has the lowest standard reduction potential (-5[1])on the electrochemical series. This is the oxidation state of iron at the center of iron pentacarbonyl. (10[1])For 10 points, what number is the oxidation state of any pure element? (10[1])■END■ (10[3])