Litharge is $NOT$ commonly used in which of the following?

$A$ hypothetical electrochemical cell is shown below.
$A \,|\, A^{+} \,(x \ M)\, ||\, B^{+} \,(y \ M)\, |\, B$
The $emf$ measured is $+ 0.20 \ V.$ The cell reaction is

Which of the following statements regarding a mercury battery is $NOT$ true?

Explain the different conditions when an external potential is applied in the opposite direction in a galvanic cell (Voltaic cell) by taking a suitable cell example.

Which of the following metals can displace copper from a copper sulphate solution?

The following reaction occurs in a button cell:
$(i)$ $Ag_{2}O + H_{2}O + 2e^{-} \rightarrow 2Ag + 2OH^{-}$
$(ii)$ $Zn \rightarrow Zn^{2+} + 2e^{-}$
Calculate the standard Gibbs free energy change $\Delta G^{o}$ for the overall cell reaction.
$[E^{o}_{Zn^{2+}\mid Zn} = -0.76 \ V, E^{o}_{Ag_{2}O\mid Ag} = 0.34 \ V]$