How and why are dichotomous keys are used

A dichotomous key is a type of single-access key that gives only two choices at one time, These keys are commonly used in biology in order to identify an unknown animal or plant.

Dichotomous keys are very useful because they allow non-expert users to identify organisms by directing them to look at the known, important organisms.

Explanation:

answer; i believe the correct answer is (anemia);

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.