Question

Difference between crust and trough?

Answer 1

crust is the region where pressure and density is more  
trough is the region where pressure and density is less
crust is also known as compression
trough is also known as rarefraction

Answer 2

A crest is a point on the wave where the displacement of the medium is at a maximum and trough is the point on the wave where the displacement of the medium is at minimum point on cycle.