In the fountain experiment which of the following gas is used?

The correct option is D

Ammonium chloride and hydrogen chloride gas.

The explanation for the correct option:

Option (C): Ammonia and Hydrogen chloride gas.

1. This experiment is used to explain the solubility of a gas.
2. The experiment introduces concepts like solubility and gas laws. When litmus is added to the reaction mixture, it explains the alkalinity or acidity property of gases and indicates the colour change caused by the gas dissolving in water.
3. We experiment with Hydrogen chloride and Ammonia gas because both of them are soluble in water. The only difference is Ammonia is basic in nature so it turns litmus solution to blue while Hydrochloric acid is acidic in nature and turns litmus solution to red.
4. Hence, it is the correct option.

Explanation for incorrect option(s):

Option (A): Ammonia gas and Hydrogen gas

1. We cannot use hydrogen gas because it is almost insoluble in water and this experiment is done to show the solubility of a gas.
2. Hence it is an incorrect option

Option (B): Ammonia gas and Chlorine gas

1. Chlorine gas is less soluble in water and we need a gas that is highly soluble in water to demonstrate this experiment.
2. Hence, it is an incorrect option.

Option (D): Ammonium chloride and Hydrogen chloride gas

1. Hydrogen chloride gas is used in this experiment because of its high solubility and acidic nature but ammonium chloride cannot be used in this experiment because this experiment aims to tell the solubility of gas whereas ammonium chloride is a white crystalline salt.
2. Hence, it is an incorrect option.

Therefore, Hydrogen chloride gas and Ammonia gas are used in the fountain experiment.