Identifying the Greenish Yellow Gas

The question asks to identify a substance that is a greenish-yellow gas with a characteristic smell at room temperature.

Substance Properties Analysis

• Carbon monoxide (CO): This is a colorless and odorless gas, making it unsuitable.
• Iodine (I₂): Iodine is a solid at room temperature. While it can produce violet vapors when heated, it is not primarily a greenish-yellow gas under normal conditions.
• Chlorine (Cl₂): Chlorine gas is known to be greenish-yellow in color and possesses a sharp, pungent, characteristic smell. It exists as a gas at room temperature. This matches the description given.
• Hydrogen sulphide (H₂S): This gas is colorless and has a distinct smell often described as rotten eggs. It does not match the color or smell described.

Based on the physical properties, Chlorine (Cl₂) is the substance that fits the description of a greenish-yellow gas with a characteristic smell at room temperature.