What is the color of fluorine gas?

• A. Colorless
• B. Green
• C. Blue
• D. Pale yellow

Answer: (D)

Fluorine gas is a pale yellow color in the visible region, due to its F2 molecules absorbing some of the blue-green light. This pale yellow appearance is a characteristic of the halogen gases in the gas phase: fluorine is the lightest and appears pale yellow, chlorine would look greenish-yellow, bromine is a liquid that appears reddish-brown (and its vapor is yellow-brown), and iodine exhibits a violet color in its solid and vapor forms. The observed pale yellow color for fluorine gas is distinct from colorless or blue, which do not match its actual appearance at room temperature.