At room temperature, chlorine gas is best described as:

Chlorine gas, at room temperature, is accurately characterized as greenish-yellow with a pungent odor. This distinctive coloration and scent are critical for its identification, especially in contexts where chlorine is used for disinfection in water treatment processes. The greenish-yellow tint can help alert personnel to the presence of chlorine, as it is essential for safety and operational protocols. Its strong, sharp odor is also a significant feature, allowing individuals to recognize leakage or high concentrations of chlorine gas, which can be hazardous.

Understanding the properties of chlorine gas is vital for operators to ensure safety standards are maintained in water treatment facilities. Other descriptions, such as being colorless and odorless or clear and sweet-smelling, do not align with chlorine's actual characteristics and could lead to dangerous situations if mistaken.