Which of the following statements is correct?

Henry's law constant for the molality of methane in benzene at $298 \, K$ is $4.27 \times 10^{5} \, mm \, Hg$. Calculate the solubility of methane in benzene at $298 \, K$ under $760 \, mm \, Hg$.

Calculate the pressure of the gas if the solubility of the gas in water at $25^{\circ} C$ is $6.85 \times 10^{-4} \ mol \ dm^{-3}$. (Henry's law constant $K_H$ is $6.85 \times 10^{-4} \ mol \ dm^{-3} \ bar^{-1}$) (in $bar$)

Give an example of a solution where both the solute and the solvent are in the gaseous state.

Consider a solution of $CO_{2(g)}$ dissolved in water in a closed container. Which one of the following plots correctly represents the variation of $log$ (partial pressure of $CO_2$ in vapour phase above water) [y-axis] with $log$ (mole fraction of $CO_2$ in water) [x-axis] at $25^{\circ}C$?

The relation between the solubility of a gas in a liquid at a constant temperature and external pressure is stated by which law?