Chem qns help >.< ? part 3?

The above responder is correct in the second part. The first part relies on the solubilities of BaCl2 and BaSO4. BaCl2 is very soluble (and Ba is a very reactive metal) so all is well. However, BaSO4 is very insoluble, and coats the surface of the piece of metal as soon as the reaction starts, thus preventing any further reaction.