A non-metal placed below in electrochemical series displaces the non-metal placed above it from that's salt solution (ion).
A non-metal which lies below in electrochemical series is more reactive.
Greater the value of Eo, greater is the reactivity of the metal. ∴Cl2 displaces Br2 from NaBr
and I2 from NaI but does not displace F2 from NaF. Br2 displaces I2 from NaI but not Cl2 from NaCl . I2 cannot displace Cl2 or Br2 from chlorides or bromides.