Which of the following species acts as a reducing agent during the working of a hydrogen-oxygen fuel cell?

The electrochemical cell is set up as follows: $Pt (H_2, 1 \, atm) | HCl (0.1 \, M) || \text{Acetic Acid} (0.1 \, M) | (H_2, 1 \, atm) Pt$. The $E.M.F.$ of the cell is not zero because:

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:

$A$ solution containing $1 \ mol \ L^{-1}$ of each $Cu(NO_3)_2, AgNO_3, Hg_2(NO_3)_2$ and $Mg(NO_3)_2$ is being electrolysed using inert electrodes. The standard reduction potentials are $E^0_{Ag^{+}/Ag} = +0.80 \ V, E^0_{Hg_2^{2+}/Hg} = +0.79 \ V, E^0_{Cu^{2+}/Cu} = +0.34 \ V, E^0_{Mg^{2+}/Mg} = -2.37 \ V$. With increasing voltage,the sequence of deposition of metals on the cathode will be:

For a general redox reaction:
Anode: $Red_1 \to Ox_1^{n_1+} + n_1 e^-$
Cathode: $Ox_2^{n_2+} + n_2 e^- \to Red_2$
Which of the following statements is incorrect?

Which of the following is $NOT$ an example of a secondary voltaic cell?