Which of the following statements is correct?

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 $16\%$.

Give an example of a solid solution in which the solute is a gas.

How many millimoles of nitrogen dissolve when nitrogen is passed in $1 \ L$ water at $293 \ K$ temperature? $[$ The value of $K_H$ is $7.648 \times 10^4 \ bar$ and partial pressure of $N_2$ gas is $0.987 \ bar.]$

Explain the hydration of sodium chloride.

If $CO_2$ gas having a partial pressure of $1.67 \ bar$ is bubbled through $1 \ L$ water at $298 \ K$,the amount of $CO_2$ dissolved in water in $g \ L^{-1}$ is approximately. (Henry's law constant of $CO_2$ is $1.67 \ kbar$ at $298 \ K$)