In electrolysis of NaCl when Pt electrode is taken then H₂ is liberated at cathode while with Hg cathode it forms sodium amalgam

Standard electrode potentials are
Fe²⁺/Fe [E^o = $$-$$0.44] and
Fe³⁺/Fe²⁺[ E^o = 0.77];
If Fe²⁺, Fe³⁺ and Fe blocks are kept together, then

Cell reaction is spontaneous when

For the disproportionation of copper
2Cu⁺  $$ \to $$ Cu²⁺ + Cu, E^o is
(Given E^o for Cu²⁺/Cu is 0.34 V and
E^o for Cu²⁺/Cu⁺ is 0.15 V.)