$CaCO_3$ reacts with $HCl$ to produce $CaCl_2, CO_2$ and $H_2O$. The approximate mass (in $g$) of $CaCO_3$ required to react completely with $25 \ mL$ of $0.75 \ M \ HCl$ is (atomic mass of $Ca=40, C=12, O=16, Cl=35.5$ and $H=1$).

For preparing one litre $N/10$ solution of $H_2SO_4$,we need $H_2SO_4$.......$g$.

$10 \ mL$ of conc. $H_2SO_4$ $(18 \ M)$ is diluted to $1 \ L$. The approximate strength of the dilute acid is $........... \ N$.

What volume in liters is required to prepare a $0.1 \ N$ $HNO_3$ solution from $6.3 \ g$ of $HNO_3$?

The vapour density of a certain gas is $16$. What is the volume occupied by $8 \ g$ of gas at $STP$ assuming ideal behaviour (in $dm^3$)?

$A$ mixture of $CaCl_2$ and $NaCl$ weighing $4.44 \ g$ is treated with sodium carbonate solution to precipitate all the calcium ions as calcium carbonate. The calcium carbonate so obtained is heated strongly to get $0.56 \ g$ of $CaO$. The percentage of $NaCl$ in the mixture is (atomic mass of $Ca=40$)