The value of $ ext{K}_ ext{H}$ at $298 ext{ K}$ for $ ext{Ar(g)}$, $ ext{CO}_2 ext{(g)}$, $ ext{HCHO(g)}$ and $ ext{CH}_4 ext{(g)}$ are $40\cdot32$, $1\cdot68$, $1\cdot84 imes 10^{-5}$ and $0\cdot416 ext{ kbar}$ respectively. When these gases are arranged in increasing order of solubility, the correct order is : (A) $ ext{HCHO} < ext{CH}_4 < ext{CO}_2 < ext{Ar}$ (B) $ ext{HCHO} < ext{CO}_2 < ext{CH}_4 < ext{Ar}$ (C) $ ext{Ar} < ext{CO}_2 < ext{CH}_4 < ext{HCHO}$ (D) $ ext{Ar} < ext{CH}_4 < ext{CO}_2 < ext{HCHO}$