An unconformity is

a. layer of sedimentary rocks.
b. gap in the rock record.
c. intrusion.
d. layer of rock with unusual fossils.

The freezing and boiling point of a substance changes as the air pressure around it changes. for example, at a lower air pressure (higher altitude) it is easier for water molecules to escape from liquid into the air. in a high altitude city such as denver, colorado compared to a sea-level city such as houston, texas, water