What is the change in oxidation number of $Pb$ at the positive electrode of a lead accumulator acting as a galvanic cell?

How is the thermodynamic efficiency of a cell defined?

Which of the following statements is incorrect during the discharge of a lead storage battery?

$A$ fuel cell uses $CH_4$ gas and it forms $CO_3^{2-}$ at the anode. It is used to power a car with $96.5 \ A$ for $10000 \ s$. The volume of $CH_4$ gas required at $1 \ atm$ and $273 \ K$ is $............ \ L$.

The chemical reaction taking place at the anode of a cell is

Given $\lambda^{\circ}_{Mg^{2+}} = 106 \ S \ cm^2 \ mole^{-1}$ and $\lambda^{\circ}_{SO_4^{2-}} = 160 \ S \ cm^2 \ mole^{-1}$. The value of $\lambda^{\circ}_{MgSO_4}$ (in $S \ cm^2 \ mole^{-1}$) is