What happens when an air mass with a low density collides with a high density air mass?

Can someone list any possible solutions to air pollution ?

How will globalization most likely affect language around the world? no new languages will be created. nations will adopt a universal language. more languages will become extinct. english will become less prevalent. languages will grow more isolated and distinct.

Based on what you know about speed of light and sound, which come/comes first in a thunderstorm