$100 \, mL$ of $0.1 \, N \, HCl$ is neutralized by $0.2 \, N \, NaOH$ solution. After adding $30 \, mL$ of $NaOH$ solution,the neutralization is continued using $0.25 \, N \, KOH$. Calculate the volume of $KOH$ in $mL$ required to complete the neutralization.

$A$ solution of $H_2SO_4$ is $31.4 \%$ $H_2SO_4$ by mass and has a density of $1.25 \ g \ mL^{-1}$. The molarity of the $H_2SO_4$ solution is . . . . . . $M$ (nearest integer) [Given molar mass of $H_2SO_4 = 98 \ g \ mol^{-1}$]

The amount of metallic $Zn$ (atomic weight $= 65.4$) required to react with aqueous sodium hydroxide to produce $1 \ g$ of $H_2$ is $.... \ g$.

The amount of iron $(Fe)$ in $g$ which can be produced from $600 \ g$ of magnetite ore is [Atomic mass of $Fe$ : $55.8$]

$A$ $10 \ g$ effervescent tablet containing sodium bicarbonate $(NaHCO_3)$ and oxalic acid $(H_2C_2O_4)$ releases $0.25 \ L$ of $CO_2$ at $T = 298.15 \ K$ and $p = 1 \ bar$. If the molar volume of $CO_2$ is $25.0 \ L \ mol^{-1}$ under these conditions,what is the percentage by mass of sodium bicarbonate in each tablet? [Molar mass of $NaHCO_3 = 84 \ g \ mol^{-1}$,Molar mass of $H_2C_2O_4 = 90 \ g \ mol^{-1}$]

At $S.T.P.$,$1 \ g$ $CaCO_3$ on decomposition gives $CO_2$ ............. $litres$.