ANS:A - Precipitation of sulphur takes place.

When sulfur dioxide (SO2) is passed through a solution of hydrogen sulfide (H2S) in water, a precipitation reaction occurs, resulting in the formation of sulfur (S) as a solid precipitate. Here's an explanation of the process:

1. Chemical Reaction: The reaction between sulfur dioxide and hydrogen sulfide in water can be represented as follows: SO2​+H2​S→S↓+H2​SO3​
2. Formation of Sulfur Precipitate: In the reaction, sulfur dioxide (SO2) reacts with hydrogen sulfide (H2S) to form elemental sulfur (S) and sulfurous acid (H2SO3). The sulfur produced in the reaction is insoluble in water and precipitates out as a solid.
3. Appearance: The precipitated sulfur may appear as a yellowish or white solid, depending on its purity and other factors. It may settle at the bottom of the container or form fine particles suspended in the solution.
4. Observation: When sulfur dioxide is passed through a solution of hydrogen sulfide in water, the formation of sulfur precipitate can be observed visually. The appearance of a solid or cloudy material in the solution indicates the occurrence of the precipitation reaction.
5. Utility: The precipitation of sulfur can be utilized in various applications, such as the purification of gases containing sulfur compounds and the recovery of elemental sulfur from industrial processes. Additionally, the formation of sulfur precipitate may also serve as an indicator of the reaction's progress in certain chemical analyses.

In summary, the precipitation of sulfur occurs when sulfur dioxide reacts with hydrogen sulfide in water, leading to the formation of elemental sulfur as a solid precipitate. This reaction plays a role in various chemical processes and can be visually observed as the appearance of a solid material in the solution.