The standard reduction potential for Zn2+/Zn,Ni2+/Ni and Fe2+/Fe are −0.76,−0.23and -0.44 V respectively. The reaction X+Y2+⟶X2++Y will be spontaneous if

A cell reaction is spontaneous, if ΔG∘<0Since,     ΔG∘=−nFcell ∘Thus,    Ecell∘>0           Ecell ∘=Eoxi ∘+ERed∘                (a) X = Ni,  Y = Fe       Ni+Fe2+⟶Ni2++Fe      ENi/Ni2+o=0.23 VE∘Fe2+/Fe=−0.44 V   Thus,  Ecell ∘=ENi/Ni2+∘+EFe2+/Fe∘                     =-0.21 V Ecell ∘<0,reaction is non-spontaneous.(b) X = Ni, Y = Zn,     Ni+Zn2+⟶Ni2++Zn    ENi/Ni2+=0.23V,EZn2+/Zn∘=−0.76V         Ecell ∘=−0.53V    Ecell α<0 reaction is non- spontaneous.(c ) X=Fe,Y=Zn,Fe+Zn2+⟶Fe2++Zn      Ecell ∘=EFe/Fe2+∘+EZn2+/Zn∘=0.44−0.76=−0.32V     Ecell ∘<0, reaction is non- spontaneous.(d) X=Zn,Y=Ni     Zn+Ni2+⟶Zn2++Ni      Ecell ∘=EZn/Zn2+∘+ENi2+/Ni∘=0.76−0.23=0.53V    The reaction is spontaneous.