$20 \ g$ of iron pyrite,$FeS_2$,is roasted completely and the $SO_2$ gas produced is absorbed completely in $400 \ mL$ of $NaOH$ solution. If only $50\%$ of the $NaOH$ is used in the reaction,what was the molarity of the $NaOH$ solution?

$250 \ mL$ of a sodium carbonate solution contains $2.65 \ g$ of $Na_2CO_3$. If $10 \ mL$ of this solution is diluted to $1 \ L$,what is the concentration of the resultant solution (in $M$)?

Reaction of $x \ g$ of $Sn$ with $HCl$ quantitatively produced a salt. The entire amount of the salt reacted with $y \ g$ of nitrobenzene in the presence of the required amount of $HCl$ to produce $1.29 \ g$ of an organic salt (anilinium chloride) quantitatively.
$(1)$ The value of $x$ is. . . . .
$(2)$ The value of $y$ is. . . . .

If $1/2 \text{ mole of oxygen reacts with aluminum to form } Al_2O_3, \text{ the mass of aluminum metal consumed in the reaction is } ..... \text{ g. } (Al=27)$

If $2 \ g$ of $NaOH$ is dissolved in water to make a $100 \ cm^3$ solution,what is the normality of this solution?

If $10 \ g$ ($90 \%$ pure) limestone is heated,what volume of $CO_2$ in liters will be obtained at $NTP$?