An unknown compound A has been prepared from the reaction of dehalogenation of a tetra halo derivative with zinc and  B is its positional isomer.  B gives a white precipitate with ammoniacal Silver nitrate but not A. A and B maybe

[Step 1]: dehalogenation of tetra halo derivative with zinc will give alkyne or dienes[Step 2]: Terminal Alkynes gives white precipitate with ammoniacal Silver nitrate whereas internal Alkynes won’t. It indicates that A is internal alkyne and B is terminal alkyne