15. The field of ___ focuses on identifying the role any substances may
have played in an illness or death.

Toxicology

Explanation:

The Field of Toxicolgy deals with the with the nature, effects, and detection of poisons

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.