$A$ cell reaction is spontaneous when:

$A$ cell is constructed by dipping a copper rod in $1\,M\,CuSO_4$ solution and a nickel rod in $1\,M\,NiSO_4$ solution. The standard reduction potentials of copper and nickel electrodes are $+0.34\,V$ and $-0.25\,V$ respectively. Calculate the $EMF$ of the cell. (in $,V$)

The standard reduction potentials at $298 \ K$ for the following half-reactions are given:
$Zn^{2+}_{(aq)} + 2e^- \rightleftharpoons Zn_{(s)}; E^\circ = -0.762 \ V$
$Cr^{3+}_{(aq)} + 3e^- \rightleftharpoons Cr_{(s)}; E^\circ = -0.740 \ V$
$2H^+_{(aq)} + 2e^- \rightleftharpoons H_{2(g)}; E^\circ = 0.00 \ V$
$Fe^{3+}_{(aq)} + e^- \rightleftharpoons Fe^{2+}_{(aq)}; E^\circ = 0.770 \ V$
Which is the strongest reducing agent?

$(i)$ Copper metal dissolves in $1 \ M$ silver nitrate solution and crystals of silver metal get deposited.
$(ii)$ Silver metal does not react with $1 \ M$ zinc nitrate solution.
$(iii)$ Zinc metal dissolves in $1 \ M$ copper sulphate solution and copper metal gets deposited.
Hence,the order of decreasing strength of the three metals as reducing agents will be:

What is the observation we get when a gold ring is placed in the solution of $AgNO_3$? $[E_{Ag^{+}|Ag}^o = 0.80 \ V$ and $E_{Au^{3+}|Au}^o = 1.40 \ V]$

Consider the following cell:
$Zn_{(s)} \mid Zn^{2+}_{(1M)} \parallel KCl_{(sat)} \mid Hg_2Cl_{2(paste)} \mid Hg$
$E^{\circ}_{cell} = 1.007 \ V$ and $E^{\circ}_{calomel} = 0.242 \ V$
What is the standard potential of $Zn$ (in $V$)?