Which one of the following statements is incorrect in Fe₄ efficiency thrice a ligand and satisfied only the secondary valency of ferrous iron? 1) The efficiency of Fe₄ is thrice that of a ligand 2) The efficiency of Fe₄ satisfies only the secondary valency of ferrous iron 3) The efficiency of Fe₄ is satisfied by both primary and secondary valency of ferrous iron 4) The efficiency of Fe₄ is satisfied by only the primary valency of ferrous iron
