Equal masses in grams of $H_2$, $N_2$, $Cl_2$, and $O_2$ are enclosed in cylinders separately. If these gases expand isothermally and reversibly by $10 \ dm^3$ at $300 \ K$, the work done by the gas is maximum for:

$10 \ g$ 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 $............ \%$.

As per the following equation, $0.217 \ g$ of $HgO$ (molecular mass $= 217 \ g \ mol^{-1}$) reacts with excess iodide. On titration of the resulting solution, how many $mL$ of $0.01 \ M$ $HCl$ is required to reach the equivalence point (in $mL$)?
$HgO + 4 I^{-} + H_2O \longrightarrow HgI_4^{2-} + 2 OH^{-}$

Concentrated sulfuric acid is $95\%$ by weight and its density is $1.8 \ g \ cm^{-3}$. What volume of concentrated acid in $cm^3$ is required to prepare $4 \ L$ of $0.4 \ M \ H_2SO_4$ solution (in $.7$)?

Equal masses of $H_2, O_2$ and methane have been taken in a container of volume $V$ at temperature $27 \ ^oC$ in identical conditions. The ratio of the volumes of gases $H_2 : O_2 :$ methane would be

$5\, g$ of benzene on nitration gave $6.6\, g$ of nitrobenzene. The theoretical yield of the nitrobenzene will be $..............$ $g$.