$20 \ mL$ of $CO_2$ gas are passed over excess of red hot coke. The volume of $CO$ evolved is ............. $mL$.
$CO_{2(g)} + C_{(s)} \to 2CO_{(g)}$

$10 \, L$ solution of urea contains $240 \, g$ urea. The active mass of urea will be

Equal weights of ethane and hydrogen are mixed in an empty container at $25^{\circ} C$. The fraction of total pressure exerted by hydrogen is

Some $CO_2$ gas was kept in a sealed container at a pressure of $1 \ atm$ and at $273 \ K$. This entire amount of $CO_2$ gas was later passed through an aqueous solution of $Ca(OH)_2$. The excess unreacted $Ca(OH)_2$ was later neutralized with $0.1 \ M$ of $40 \ mL$ $HCl$. If the volume of the sealed container of $CO_2$ was $x$,then $x$ is $............. \ cm^3$ $(nearest \ integer)$.
$[$Given : The entire amount of $CO_{2(g)}$ reacted with exactly half the initial amount of $Ca(OH)_2$ present in the aqueous solution.$]$

What is the weight (in $g$) of $Na_2CO_3$ (molar mass $= 106$) present in $250 \ mL$ of its $0.2 \ M$ solution?

What will be the weight of lime $(CaO)$ obtained by heating $300 \ kg$ of $90\%$ pure limestone $(CaCO_3)$?