The amount of anhydrous $Na_2CO_3$ present in $250 \ mL$ of $0.25 \ M$ solution is ........ $g$.

$P_4O_6$ reacts with water according to the equation $P_4O_6 + 6H_2O \to 4H_3PO_3$. Calculate the volume of $0.1 \ M$ $NaOH$ solution required to neutralize the acid formed by dissolving $1.1 \ g$ of $P_4O_6$ in $H_2O$. (in $mL$)

$A$ solution contains $1.2046 \times 10^{24}$ hydrochloric acid molecules in one $dm^3$ of the solution. The strength of the solution is .......... $N$.

The hardness of a water sample (in terms of equivalents of $CaCO_3$) containing $10^{-3} \ M \ CaSO_4$ is ................... $ppm$ (Molecular mass of $CaSO_4 = 136 \ g \ mol^{-1}$)

$20 \ g$ 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?

While combusting in air, $4 \ g$ of $H_2$ gas was completely converted into water. If $36 \ \mu mole$ of $CO_2$ from air is dissolved into that water, what is the concentration of $CO_2$?