Check all the characteristics below that describe
elements
one type of atom
a pure substance
more than one type of atom
chemically combined elements

A pure substance, only one type of atom

Explanation:

The Answer your looking for is A and B

A-one type of atom

B- a pure substance

Explanation:

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.