Which is the most accurate description of compounds?
a. they are not pure substances.
b. they are made of only 1 type of atom.
c. they are the basic building blocks of matter.
d. they are made up of atoms of 2 or more elements that are chemically combined.

Option (d) is the correct answer.

Explanation:

A compound is defined as the substance in which only different atoms chemically combine together in a fixed ratio by mass.

For example, NaCl, HCl, , etc are all compounds.

Compounds are also pure substances like elements as they can be broken down into their constituent particles.

Whereas substances that are made up of only one type of atom are known as elements.

Thus, we can conclude that the most accurate description of compounds is that they are made up of atoms of 2 or more elements that are chemically combined.

geosphere and hydrosphere.

this is because the geosphere has to do with geological events, while the hydrosphere controls all water on earth.