$20 \ g$ of hydrogen gas $(H_2)$ is present in a $5 \ L$ vessel. The molar concentration of hydrogen is: (in $M$)

$23 \ g$ of $Na$ will react with methyl alcohol to give:

$30.0 \ mL$ of the given $HCl$ solution requires $20.0 \ mL$ of $0.1 \ M$ sodium carbonate solution for complete neutralisation. What is the volume of this $HCl$ solution required to neutralise $30.0 \ mL$ of $0.2 \ M$ $NaOH$ solution (in $mL$)?

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 $dm^3$)?

......... $cm^3$ is the volume of $0.1 \ N \ HCl$ required to react completely with $1.0 \ g$ of pure calcium carbonate $(Ca = 40, C = 12, O = 16)$.

What is the weight of $H_2SO_4$ (in $g$) required to completely dissolve $3 \ g$ of magnesium carbonate?