The standard reduction potentials for Zn²⁺/ Zn, Ni²⁺/ Ni, and Fe²⁺/ Fe are –0.76, –0.23 and –0.44 V respectively. The reaction

X + Y²⁺ $$\to$$ X²⁺ + Y will be spontaneous when :

The reduction potential of hydrogen half cell will be negative if :

The correct order of $$E_{{M^{2 + }}/M}^o$$ values with negative sign for the four successive elements Cr, Mn, Fe and Co is :

The Gibbs energy for the decomposition of Al₂O₃ at 500^oC is as follows :

$${2 \over 3}A{l_2}{O_3}$$ $$\to$$ $${4 \over 3}Al + {O_2}$$, $${\Delta _r}G$$ = + 966 kJ mol^–1

The potential difference needed for electrolytic reduction of Al₂O₃ at 500^oC is at least :