Question

What is the opposite of rarefaction zones, where air molecules in waves are loosely packed?

Answer 1

compression zones

Longitudinal waves, like sound waves, have compression and rarefaction zones. The compression zones are where, for example in a sound wave traveling through air, the air molecules are densely packed. The rarefaction zones are areas where the air molecules are loosely packed, like a vacuum zone. Us teachers will often draw longitudinal waves as transverse waves, but remember the difference.