Answer:
D. 3H2O
Step-by-step explanation:
An atom is the smallest unit of matter that has the characteristics of a chemical element. It consists of protons, neutrons, and electrons - small electrically charged particles.
They make up molecules - electrically neutral groups of two or more atoms connected by chemical bonds. Multiple molecules that consist of two or more different atoms make up a chemical compound.
The chemical compound that has nine atoms is 3H2O. Here, we have three molecules of water. Each molecule consists of three atoms - two hydrogen atoms and one oxygen atom. This means that three of these molecules have a total of nine atoms.