How many grams of zinc are required to produce $224 \ mL$ of hydrogen from dilute $H_2SO_4$ at $STP$?

The density of a monobasic strong acid (Molar mass $24.2 \ g \ mol^{-1}$) is $1.21 \ kg \ L^{-1}$. The volume of its solution required for the complete neutralization of $25 \ mL$ of $0.24 \ M \ NaOH$ is $.............. \times 10^{-2} \ mL$ (Nearest integer).

If $1 \, mole$ of $H_3PO_x$ is completely neutralized by $80 \, g$ of $NaOH$,select the correct statement :-

$19 \ g$ of a mixture containing $NaHCO_3$ and $Na_2CO_3$ on complete heating liberated $1.12 \ L$ of $CO_2$ at $STP$. The weight of the remaining solid was $15.9 \ g$. What is the weight (in $g$) of $Na_2CO_3$ in the mixture before heating?

When $10 \ mol$ of $SO_2$ and $15 \ mol$ of $O_2$ are mixed and passed over a catalyst,$8 \ mol$ of $SO_3$ is formed. How many moles of $SO_2$ and $O_2$ remain unreacted?

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