What is the weight of carbon in $kg$ required to produce $270 \ kg$ of aluminum from bauxite by the Hall-Heroult process?

$15 \ mL$ of $0.2 \ N$ alkali is required to complete neutralization of $30 \ mL$ acid solution. The concentration of the acid solution is ..... $N$.

$10 \ g$ of a piece of marble $(CaCO_3)$ was put into excess of dilute $HCl$ acid. When the reaction was complete,$1120 \ mL$ of $CO_2$ was obtained at $STP$. The percentage of pure $CaCO_3$ in the marble is $............ \%$.

If $0.4 \ g$ of $NaOH$ is present in $40 \ mL$ of solution,what will be the molarity and normality? (Molecular weight of $NaOH = 40$)

The molarity of a $NaOH$ solution prepared by dissolving $4 \ g$ of it in $250 \ mL$ of water is: (in $M$)

When $3 \ g$ of $C_2H_6$ is completely burnt,find out the volume of $CO_2$ produced at $STP$ in $L$.