Which one of the following statements is true for a standard electrochemical cell involving $H_2$ and $Cu$ electrodes?

If $\lambda_{m}^{o}(Br^{-}) = 78.1 \, S \, cm^{2} \, mol^{-1}$,calculate $\lambda_{m}^{o}(K^{+})$ using the following data:

Electrolyte	$\Lambda_{m}^{o} \, (S \, cm^{2} \, mol^{-1})$
$NaCl$	$126.5$
$NaBr$	$128.2$
$KCl$	$149.5$

The standard cell potential $(E_{\text{cell}}^{\ominus})$ of a fuel cell based on the oxidation of methanol in air that has been used to power television relay station is measured as $1.21 \ V$. The standard half-cell reduction potential for $O_2$ $(E_{O_2 / H_2 O}^0)$ is $1.229 \ V$. Choose the correct statement:

When a $Cu$ rod is kept in an $AgNO_3$ solution,what is the redox reaction that occurs?

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 $:$