Explanation

(b)
Standard oxidation potentials of Zn, Cu, Ag and Ni electrode are + 0.76, - 0.34, - 0.80 and + 0.25 V respectively. (Given)
${Zn}^{2 +}\ + \ {2e}^{-}\ \rightarrow \ Zn\ ;\ \ \ \ \ \ \$ $E_{cell}$ = - 0.76 V
${Cu}^{2 +}\ + \ {2e}^{-}\ \rightarrow \ Cu\ ;$ $E_{cell}$ = + 0.34 V
${Ag}^{+}\ + \ e^{-}\ \rightarrow \ Ag\ ;$ $E_{cell}$ = + 0.80 V
${Ni}^{2 +}\ + \ {2e}^{-} \rightarrow \ Ni\ ;\ \ \ \$ $E_{cell}$ = - 0.25 V
$Cu\ + \ 2Ag\ (aq)\ \rightarrow \ {Cu}^{2 +}\ (aq)\ + \ 2\ Ag$
$E_{cell}^{{^\circ}} = \ E_{cathode}^{{^\circ}}\ - \ E_{anode}^{{^\circ}}$
$E_{cell} = \ 0.80\ –\ 0.34\ = \ 0.46\ V$
$Zn\ + \ 2\ {Ag}^{+}\ (aq)\ \rightarrow \ {Zn}^{2 +}\ (aq)\ + \ 2\ Ag$
$E_{cell}\ = \ 0.80\ –\ ( - \ 0.76)\ = \ 1.56\ V$
$\ \ \ \ \ \ \ \ \ \ \ \$ (maximum voltage)
$\ H_{2}\ + \ {Ni}^{2 +}\ (aq)\ \rightarrow \ {2H}^{+}\ (aq)\ + \ Ni$
$E_{cell}\ = \ - \ 0.25\ V$
$Zn\ + \ {Cu}^{2 +}\ (aq)\ \rightarrow \ {Zn}^{2 +}\ (aq)\ + \ Cu$
$E_{cell}\ = \ 0.34\ –\ (\ - \ 0.76)\ = \ 1.00\ V$
$\ Zn\ + \ 2\ H^{+}\ (aq)\ \rightarrow \ {Zn}^{2 +}\ (aq)\ + \ H_{2}$
$E_{cell}\ = \ 0\ –\ (\ 0.76\ V)\ = \ 0.76\ V$