Which one of following acts as Lewis acid but not as a Lewis base

1)C..-≡O..+ is a strong ligand, a Lewis base but not a Lewis acid;2)S¨O2, S¨Cl4...contain lone pair on cental atom thus act like Lewis base ;They can expand valency thus act like Lewis acid ;3)PF5...can expand valency thus Lewis acid;No lone pair on central atom thus cannot act like Lewis base ;