Which of the following statements is $NOT$ correct?

In a fuel cell,methanol is used as fuel and oxygen gas is used as an oxidizer. The reaction is
$CH_3OH_{(l)} + \frac{3}{2} O_{2(g)} \rightarrow CO_{2(g)} + 2H_2O_{(l)}$
At $298 \ K$,standard Gibbs energies of formation for $CH_3OH_{(l)}$,$H_2O_{(l)}$,and $CO_{2(g)}$ are $-166.2$,$-237.2$,and $-394.4 \ kJ \ mol^{-1}$ respectively. If the standard enthalpy of combustion of methanol is $-726 \ kJ \ mol^{-1}$,the efficiency of the fuel cell will be .......... $\%$.

During the electrolysis of concentrated $H_2SO_4$,perdisulphuric acid $(H_2S_2O_8)$ and $O_2$ are formed at the anode in equimolar amounts. The moles of $H_2$ that will form simultaneously at the other electrode will be (Given: $2H_2SO_4 \rightarrow H_2S_2O_8 + 2H^+ + 2e^-$)

Molar conductances of $BaCl_2$,$H_2SO_4$,and $HCl$ at infinite dilutions are $x_1, x_2$,and $x_3$,respectively. Equivalent conductance of $BaSO_4$ at infinite dilution will be

$100 \text{ mL}$ of $0.2 \text{ M}$ acetic acid is completely neutralized using a standard solution of $NaOH$. The volume of ethane obtained at $STP$ after complete electrolysis of the resulting solution is: (in $\text{ L}$)

Calculate the $K_C$ and $\Delta G^o$ for the chemical reaction :
$Ni_{(s)} + 2Ag_{(aq)}^{+} \to Ni_{(aq)}^{2+} + 2Ag_{(s)}$ $ [E^o = 1.05 \, V] $