Which of the following gases at 298 K and 1 atm pressure is having maximum solubility in water?

Methanal, $K_H= 0.000018$

The correct answer is Option (1) → Methanal, $K_H= 0.000018$.

The solubility of gases in water can be determined using Henry's law, which states that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid. The constant of proportionality is known as the Henry’s law constant (\( K_H \)).

According to Henry's law:

\(S = \frac{P}{K_H}\

Where:

\( S \) is the solubility of the gas,

\( P \) is the partial pressure of the gas,

\( K_H \) is the Henry's law constant.

Understanding \( K_H \):

A smaller \( K_H \) value indicates greater solubility because the inverse of \( K_H \) is used to calculate solubility (\( S \)).

A larger \( K_H \) value indicates lower solubility.

Given \( K_H \) values:

1. Methanal (HCHO): \( K_H = 0.000018 \)

2. Argon (Ar): \( K_H = 40.3 \)

3. Methane (CH₄): \( K_H = 0.41 \)

4. Carbon dioxide (CO₂): \( K_H = 1.6 \)

Conclusion:

Methanal (HCHO) has the smallest \( K_H \) value of \( 0.000018 \), which means it has the highest solubility in water.

Thus, the gas with the maximum solubility in water is Methanal