A drop of liquid bromine is placed in the bottom of a gas jar. Brown fumes of bromine vapour slowly spread through the covered gas jar.
Why does this happen?
A: Bromine vapour is less dense than air.
B: Bromine molecules and the molecules in air are always moving around.
C: Bromine molecules are smaller than the molecules in air.
D: Bromine molecules move faster than the molecules in air.