At $293 \ K$,methane gas was passed into $1 \ L$ of water. The partial pressure of methane is $1 \ bar$. The number of moles of methane dissolved in $1 \ L$ water is ($K_{H}$ of methane $= 0.4 \ kbar$)

Henry's law constant for $CO_{2}$ in water is $1.67 \times 10^{8} \ Pa$ at $298 \ K$. Calculate the quantity of $CO_{2}$ in $500 \ mL$ of soda water when packed under $2.5 \ atm$ $CO_{2}$ pressure at $298 \ K$.

How many grams of water are required to dissolve $4 \ g$ of sodium sulfate at $323 \ K$? The solubility of sodium sulfate at this temperature is $16\%$.

Why is a mixture of $He-O_2$ used by deep-sea divers instead of a $N_2-O_2$ mixture?

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: Helium is used to dilute oxygen in diving apparatus.
Reason $R$: Helium has high solubility in $O_2$.
In the light of the above statements,choose the correct answer from the options given below:

$A$ gas $X$ is dissolved in water at $2 \ bar$ pressure. Its mole fraction in the solution is $0.02$. Find the mole fraction of water in the solution when the pressure of the gas is doubled at the same temperature.