What is the volume occupied by $2 \ g$ of helium gas at $STP$ (in $dm^3$)? (molar mass of helium gas $= 4 \ g \ mol^{-1}$)

$40\%$ of a mixture of $0.2 \ mol$ of $N_2$ and $0.6 \ mol$ of $H_2$ reacts to give $NH_3$ according to the equation:
$N_{2(g)} + 3H_{2(g)} \rightleftharpoons 2NH_{3(g)}$
at constant temperature and pressure. What is the ratio of the final volume to the initial volume of gases?

How many $mL$ of $0.1\, M\, HCl$ are required to react completely with $1\, g$ mixture of $Na_2CO_3$ and $NaHCO_3$ containing equimolar amounts of both?

To change the strength of $25 \, mL$ of $0.15 \, M$ $HCl$ to $0.1 \, M$,the quantity of water that is to be added is.......$mL$

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

The amount of carbon dioxide evolved upon complete combustion of $116 \ g$ of $n$-butane is
(Given : atomic mass in amu $H = 1, C = 12$ and $O = 16$) (in $g$)