Under what  is ${\text{E}}_{\text{Cell}}^{\text{o}}=0$ and $${\text{\Delta }}{{\text{G}}^{\text{o}}} = 0$$ ?

If $E_{CI{O}_3/CI{O}_4}^0=0.36V$ and $E_{CI{O}_3/CI{O}_2}^0=0.33V$ at $300K$.The equilibrium concentration of perchlorate ion $(CI{O}_4^{-})$ which was initially $1.0$M in $CI{O}_3^{-}$ when the reaction starts to attains the equilibrium ,
$$2ClO_^- \rightleftharpoons CIO_3^-+ClO_4^-$$
Given :$AL(0.509)=3.329$