The standard reduction potential for Zn ²⁺ / Zn , Ni ²⁺ / Ni and Fe ²⁺ / Fe are -0.76 , -0.23 and -0.44 V , respectively. The reaction X+Y²⁺ X²⁺+Y will be spontaneous when

Step-by-step solution

The reaction is spontaneous when G 0 and E_ cell ^ 0 . aligned & G=-n F E^ and E^ 0 & Also E_ cell ^ =E_ oxi ^ +E_ red ^ (or) E_ cathode ^ -E_ anode ^ aligned Here, Thus, E_ cell ^ for (a) -0.21 V , i.e. E_ cell ^0 0 (b) -0.53 V , i.e. E_ cell ^0 0 (c) -0.32 V , i.e. E_ cell ^ 0 (d) 0.53 V , i.e. E^ 0