Arrange the following gases in the increasing order of their solubility in water at 298 K and atmospheric pressure.

(A) $CH_4 (K_H = 0.413\, kbar)$
(B) $HCHO (K_H = 1.83 × 10^{-5}\, kbar)$
(C) $He (K_H = 144.97\, kbar)$
(D) $CO_2 (K_H = 1.67\, kbar)$

Choose the correct answer from the options given below:

(C), (D), (A), (B)

The correct answer is Option (2) → (C), (D), (A), (B)

The solubility of a gas in water is inversely proportional to its Henry’s law constant ($K_H$):

$\text{Higher } K_H ⇒\text{lower solubility}$

Given $K_H$ values (in kbar):

• CH₄ → 0.413
• HCHO → 1.83 × 10^-5
• He → 144.97
• CO₂ → 1.67

Now arrange increasing solubility (lowest solubility → highest solubility):

1. He ($K_H$ = 144.97) → least soluble
2. CO₂ ($K_H$ = 1.67) → more soluble
3. CH₄ ($K_H$ = 0.413) → even more soluble
4. HCHO ($K_H$ = 1.83 × 10^-5) → most soluble

Correct order (increasing solubility): (C), (D), (A), (B)