What acts as a reducing agent when a dry cell is working?

On charging the lead storage battery,the oxidation state of lead changes from $x_1$ to $y_1$ at the anode and from $x_2$ to $y_2$ at the cathode. The values of $x_1, y_1, x_2, y_2$ are respectively $:$

What is a battery?

An electrochemical cell is constructed using half-cells in the direction of spontaneous change: $Fe(OH)_{2}(s) + 2e^{-} \rightarrow Fe(s) + 2OH^{-}(aq)$ $(E^{0} = -0.88 \text{ V})$ and $AgBr(s) + e^{-} \rightarrow Ag(s) + Br^{-}(aq)$ $(E^{0} = +0.07 \text{ V})$. Which of the following options is correct?

What advantage do the fuel cells have over primary and secondary batteries?

In which of the following solutions will a blue color appear after some time when a piece of $Cu$ metal is added?