A gas jar containing bromine vapour is placed above a jar of air. After some time, John sees the brown colour spreads downward. What explains this?

An atom of fluorine has atomic number 9 and mass number 19. What are the subatomic particles in F⁻?

Water and ethanol are both liquids. John wonders why does ethanol evaporate faster?

Xinyi is doing an experiment. A cotton wool soaked in concentrated hydrochloric acid is placed at one end of a glass tube and another soaked in ammonia at the other. A white ring forms closer to the HCl end. Why?