The cells which can be recharged are:

Calculate $\Delta_r G^o$ for the cell reaction:
$Zn_{(s)} + Cu^{2+}_{(aq)} \to Zn^{2+}_{(aq)} + Cu_{(s)}$
Given: $E^o_{Cu^{2+}/Cu} = 0.34 \, V, E^o_{Zn^{2+}/Zn} = -0.76 \, V$

$A$ variable,opposite external potential $(E_{ext})$ is applied to the cell $Zn | Zn^{2+} (1 \ M) || Cu^{2+} (1 \ M) | Cu$ of potential $1.1 \ V$. When $E_{ext} < 1.1 \ V$ and $E_{ext} > 1.1 \ V$,respectively,electrons flow from:

Upon dipping a copper rod into an aqueous solution of the salt,the solution that turns blue is

From a solution of $CuSO_4$,the metal used to recover copper is

Zinc displaces copper from the solution of its salt because