Given the reaction: Zn(s) + 2 HCl(aq) → ZnCl2(aq) + H2(g)
Which statement correctly describes what occurs when this reaction takes place in a closed system?

(1) Atoms of Zn(s) lose electrons and are oxidized.
(2) Atoms of Zn(s) gain electrons and are reduced.
(3) There is a net loss of mass.
(4) There is a net gain of mass.