Which one of the following metals will not reduce $H_2O$?

In the cell represented as $Ni_{(s)}|Ni_{(1M)}^{2+}||Ag_{(1M)}^{+}|Ag_{(s)}$,the reducing agent is

At $298 \ K$,the standard electrode potentials of $Cu^{2+}/Cu$,$Zn^{2+}/Zn$,$Fe^{2+}/Fe$ and $Ag^{+}/Ag$ are $0.34 \ V$,$-0.76 \ V$,$-0.44 \ V$ and $0.80 \ V$,respectively. On the basis of standard electrode potential,predict which of the following reactions cannot occur?

$A$ galvanic cell has an electrical potential of $1.1 \ V$. If an opposing potential of $1.1 \ V$ is applied to this cell,what will happen to the cell reaction and the current flowing through the cell?

Colourless solutions of the following four salts are placed separately in four different test tubes and a strip of copper is dipped in each one of these. Which solution will turn Blue?

The Gibbs energy for the decomposition of $Al_2O_3$ at $500\,^oC$ is as follows:
$\frac{2}{3}Al_2O_3 \to \frac{4}{3}Al + O_2, \Delta_rG = +940\,kJ\,mol^{-1}$
The potential difference needed for the electrolytic reduction of aluminium oxide is ............... $V$.