The correct answer is Atoms. Atoms are the basic building blocks of all matter. Everything around us — solids, liquids, and gases — is made up of atoms. An atom is the smallest unit of an element that still keeps the properties of that element.

Atoms are made up of even smaller particles called subatomic particles: protons, neutrons, and electrons. These come together to form the atom, but the atom itself is what builds matter.

Protons and neutrons are located in the center of the atom, which is called the nucleus. Electrons move around the nucleus in orbits. Even though atoms are extremely small and cannot be seen with the naked eye, they are the foundation of all physical things.

When atoms join together, they can form molecules. For example, two hydrogen atoms and one oxygen atom form a water molecule (H₂O). But the molecule is made of atoms, so atoms come first.

In short, atoms are the smallest units that make up matter. Understanding atoms helps us understand the structure and behavior of everything we see and touch in our daily life.