Which statements are true about molecules? Select all that apply.
A. They are a group of atoms that are strongly joined.
B. They always contain only one type of atom.
C. They always contain different types of atoms.
D. They are the smallest unit of an element or a compound.

chemical weathering

explanation:

correct answer is option a.

tropopause, stratopause and mesopause have all in common aspect that is point of maximum temperature in its layer of the atmosphere. all layers of atmosphere observe abrupt change in temperature. tropopause is the boundary between troposphere and stratosphere. stratopause is the boundary between stratosphere and mesosphere. mesopause is the boundary between mesosphere and thermosphere. these all boundaries are ranges between altitude of 0 to 80 km.