When will be the solubility of gas in liquid increases?

When pressure increased.

 The answer is (4) when pressure increased.

The solubility of a gas in a liquid is directly proportional to the pressure of the gas above the liquid. This is because the pressure of the gas pushes the gas molecules into the liquid.

As the pressure of the gas increases, more gas molecules will be pushed into the liquid, and the solubility of the gas will increase.

The other options are incorrect. The solubility of a gas in a liquid decreases as the temperature of the liquid increases. This is because the kinetic energy of the gas molecules increases as the temperature increases. As a result, the gas molecules are more likely to escape from the liquid.

Therefore, the only option that will increase the solubility of a gas in a liquid is an increase in pressure.