Which one of the following gases has the lowest value of Henry’s law constant? 

$$\begin{gathered} {\mathrm{K}}_{\mathrm{H}}\left({\mathrm{N}}_2\right) = 76.48(\mathrm{K} \mathrm{bar}) \\ {\mathrm{K}}_{\mathrm{H}} \left(\mathrm{He}\right) = 144.97 \\ {\mathrm{K}}_{\mathrm{H}} \left({\mathrm{CO}}_2\right) = 1.67 \\ {\mathrm{K}}_{\mathrm{H}} \left({\mathrm{O}}_2\right) = 34.86 \end{gathered}$$

Most water soluble gas will have lesser Henry's constant.