Whats the answer? can you explain it?

Question

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

Answer 1

Bromine is much more dense than air (all gases have same volume at a T and P, and Bromine atoms have more mass --- greater density). Bromine atom size compared to air is irrelevant. Bromine molecules do not move faster as they are more massive than diatomic N or O which is most of air. v is inverse with square root of M. that leaves B which is not that great an answer. The Bromine liquid will will vaporize because there is no bromine in the air initially (so moving to equilibrium between phases requires some Br to vaporize). Finally, the Bromine will diffuse because random motion of the air and Br leads to diffusion and mixing. The Bromine will actually be more concentrated at the bottom of the container because the gas is more dense than air.