K_H value for Ar(g), CO₂ (g), HCHO(g) and CH₄ (g) are 4.039, $1.83\times {10}^{-5}$ and 0.143, respectively. Arrange these gases in the order of their increasing solubility

According to Henry's law,

$\begin{array}{r}\mathrm{P}={\mathrm{K}}_{\mathrm{H}}\mathrm{C}\\ {\mathrm{K}}_{\mathrm{H}}\propto \frac{1}{\mathrm{C}}\end{array}$

Where P = Partial pressure of gas
C = Concentration of gas
K_H = Henry's constant
It implies that as the value of K_H increases, mole fraction of gas solute in solvent decreases.
Hence, higher the K_H value, lower is the solubility of gas.
The order of increasing solubility of gases in :

$\mathrm{Ar}<{\mathrm{CO}}_2<{\mathrm{CH}}_4<\mathrm{HCHO}$