Spontaneity of a cell reaction, or the best electrode pair, from standard reduction potentials

1. A.
   ${Zn}_{(s)} + {Mg}_{(aq)}^{+ 2} \longrightarrow {Zn}_{(aq)}^{+ 2} + {Mg}_{(s)}$
2. B.
   $\ 2{Ag}_{(s)} + {Zn}_{(aq)}^{+ 2} \longrightarrow 2{Ag}^{+}\ _{(aq)} + {Zn}_{(s)}$
3. C.
   ${Zn}_{(s)} + {Cu}_{(eq)}^{+ 2} \longrightarrow {Zn}_{(eq)}^{+ 2} + {Cu}_{(s)}$
4. D.
   $\ {Cu}_{(s)} + {Mg}_{(aq)}^{+ 2} \longrightarrow {Cu}_{(aq)}^{+ 2} + {Mg}_{(s)}$

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1. A.
   $\mathrm{Ca(s) + Cd^{2+}(aq) \rightarrow Ca^{2+}(aq) + Cd(s)}$, $[E^0_{\mathrm{Ca}} = -2.866$ V & $E^0_{\mathrm{Cd}} = -0.403$ V$]$
2. B.
   $\mathrm{2Br^-(s) + Sn^{2+}(aq) \rightarrow Br_2(l) + Sn(s)}$, $[E^0_{\mathrm{Br}} = 1.08$ V & $E^0_{\mathrm{Sn}} = -0.136$ V$]$
3. C.
   $\mathrm{2Ag(s) + Ni^{2+}(aq) \rightarrow 2Ag^+(aq) + Ni(s)}$, $[E^0_{\mathrm{Ag}} = 0.799$ V & $E^0_{\mathrm{Ni}} = -0.257$ V$]$
4. D.
   $\mathrm{2Au(s) + Zn^{2+}(aq) \rightarrow 2Au^+(aq) + Zn(s)}$, $[E^0_{\mathrm{Au}} = 1.68$ V & $E^0_{\mathrm{Zn}} = -0.763$ V$]$

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1. A.
   $\mathrm{2Ag_{(s)} + Fe^{+2}_{(aq)} \rightarrow 2Ag^{+1}_{(aq)} + Fe_{(s)}}$
2. B.
   $\mathrm{2Al_{(s)} + 3Cu^{+2}_{(aq)} \rightarrow 2Al^{+3}_{(aq)} + 3Cu_{(s)}}$
3. C.
   $\mathrm{Fe_{(s)} + Cu^{+2}_{(aq)} \rightarrow Fe^{+2}_{(aq)} + Cu_{(s)}}$
4. D.
   $\mathrm{2Al_{(s)} + 3Fe^{+2}_{(aq)} \rightarrow 2Al^{+3}_{(aq)} + 3Fe_{(s)}}$

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1. A.
   X = Ni , Y = Fe
2. B.
   X = Ni , Y = Zn
3. C.
   X = Fe , Y = Zn
4. D.
   X = Zn , Y = Ni

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1. A.
   'A' is anode and 'B' is cathode
2. B.
   'B' is anode and 'D' is cathode
3. C.
   'C' is anode and 'B' is cathode
4. D.
   'B' is anode and 'C' is cathode

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