How many litres of oxygen (at $STP$) are required for complete combustion of $39 \ g$ of liquid benzene?
(Atomic weights: $C=12, O=16, H=1$)

$20 \, mL$ of $1 \, N \, KMnO_4$ solution reacts with $20 \, mL$ of oxalic acid solution. The weight of oxalic acid crystals $(H_2C_2O_4 \cdot 2H_2O)$ in the $1 \, N$ solution is . . . . . . $g$.

The concentration of a $100 \ mL$ solution containing $X \ g$ of $Na_2CO_3$ (molecular weight $= 106$) is $Y \ M$. The values of $X$ and $Y$ are respectively.

The molarity of $2 \, N \, HCl$ is .......

$A$ $240 \ mL$ mixture of $CO_2$ and $CO$ is passed over red-hot coke. The $CO_2$ is completely reduced to $CO$. When the resulting gas is brought to the same temperature and pressure,the volume becomes $300 \ mL$. What is the volume of $CO$ in the original mixture in $mL$?

The number of moles of methane required to produce $11 \ g$ of $CO_{2(g)}$ after complete combustion is:
(Given molar mass of methane in $g \ mol^{-1}: 16$)