I'm not sure what u r asking. Do u mean a reaction that is unique to only one group? I don't think such things are very common; certainly Na and other group 1 metals will react with Cl but almost anything else will as well; what sets group 1 out from all others is that it combines with Cl (and other halogens in a 1::1 ratio where group 2 combines in a 1::2 ratio ie NaCl but MgCl[sub]2[/sub]. On the other hand, group 11 shows replacement of its members; that is if u have Au ions in solution a strip of Ag will displace the Au in ions and Au crystals will form; Cu will displace Ag from solution and Ag crystals will form but Au or Ag will not displace Cu from solutions; this establishes the order of the periodic chart Cu-Ag-Au for group 11; for the halogens, solutions of NaCl, NaBr, and NaI are colorless; if u gently heat them and put F gas in the first solution. it will give NaF (slightly soluble) and liberate green Cl gas which can be sent into NaBr, which will give red-brown gas that can go into NaI which gives black crystals n violet vapor.