Answer
At the inert $Pt_{(s)}$ electrodes, mass does not change.
At the $Cu_{(s)}$ electrode, there is a mass gain through the half reaction,
$Cu^{2+}$$_{(aq.)}$ + $2e^-$ $\longrightarrow$ $Cu_{(s)}$.
At the $Zn_{(s)}$ electrode, there is a mass loss through the half reaction,
$Zn_{(s)}$ $\longrightarrow$ $2 e^-$ + $Zn^{2+}$${(aq.)}$.
Work Step by Step
At the inert $Pt_{(s)}$ electrodes, mass does not change.
At the $Cu_{(s)}$ electrode, there is a mass gain through the half reaction,
$Cu^{2+}$$_{(aq.)}$ + $2e^-$ $\longrightarrow$ $Cu_{(s)}$.
At the $Zn_{(s)}$ electrode, there is a mass loss through the half reaction,
$Zn_{(s)}$ $\longrightarrow$ $2 e^-$ + $Zn^{2+}$${(aq.)}$.
