Predict the colour of astatine solid?

• A. Black
• B. Grey
• C. White
• D. Orange

Answer: (A)

When you look at how halogens change color down the group, they get darker as you go to heavier elements. Fluorine is a pale gas, chlorine is greenish, bromine is a red-brown liquid, and iodine is a dark solid with a violet tint. Astatine is the heaviest halogen, and it's predicted to be a black solid because the trend toward darker, more metallic-like appearances continues with its greater mass and reduced ability to reflect light. It’s extremely radioactive and rare, so we don’t observe it directly, but the theoretical color is black. The other colors don’t fit this downward trend in halogen colors, so black is the best answer.