During electrolysis of aqueous $NaOH$,$4 \ g$ of $O_2$ gas is liberated at $NTP$ at the anode. The volume of $H_2$ gas liberated at the cathode in $litres$ is $..............$

Copper from copper sulphate solution can be displaced by .............. The standard reduction potentials of some electrodes are given below:
$E^o (Fe^{2+}, Fe) = -0.44 \ V$
$E^o (Zn^{2+}, Zn) = -0.76 \ V$
$E^o (Cu^{2+}, Cu) = +0.34 \ V$
$E^o (Cr^{2+}, Cr) = -0.74 \ V$
$E^o (H^{+}, 1/2H_2) = 0.00 \ V$

Match the following columns:

Column-$I$	Column-$II$
$A$. Leclanche cell (Dry cell)	$P$. Converts energy of combustion into electrical energy
$B$. Lead storage battery	$Q$. Reaction at cathode: $O_{2(g)} + 4H^+_{(aq)} + 4e^- \rightarrow 2H_2O_{(\ell)}$
$C$. Fuel cell	$R$. Reaction at cathode: $MnO_2 + NH_4^+ + e^- \rightarrow MnO(OH) + NH_3$
$D$. Rusting	$S$. Reaction at anode: $Pb_{\text{(s)}} + SO_4^{2-}{_{\text{(aq)}}} \rightarrow PbSO_{4\text{(s)}} + 2e^{-}$

The conductivity of $0.01 \ M$ aqueous acetic acid measured with a conductivity cell of cell constant $0.5 \ cm^{-1}$ at $298 \ K$ is $3.12 \times 10^{-4} \ S$. If the limiting molar conductivities of $H^{+}$ and $CH_3COO^{-}$ at the same temperature are $349$ and $41 \ S \ cm^2 \ mol^{-1}$ respectively,the dissociation constant of acetic acid is

Which one of the following statements is correct?

Which of the following is not correct?