Identify oxidation state of cobalt ion in the complex, [ Co(NH ₃)₅ Br ] SO ₄ .

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Let the oxidation state of cobalt be x . The given coordination compound dissociates into a complex cation [ Co(NH ₃)₅ Br ]²⁺ and a sulfate anion SO ₄²⁻ . The overall charge on the complex cation is +2 . Ammonia ( NH ₃ ) is a neutral ligand with an oxidation state of 0 , and bromide ( Br ^- ) has an oxidation state of -1 . Summing the oxidation states of the central metal atom and the ligands: x + 5(0) + (-1) = +2 x - 1 = +2 x = +3 The oxidation state of cobalt in the complex is +3 . Answer: +3