Yes, something can be made up of only one type of atom or particle. In fact, most of the matter around us consists of substances composed of a single type of atom. These substances are known as elements.
Elements are the building blocks of matter, and each element is characterized by the number of protons in the nucleus of its atoms, which is represented by its atomic number. For example, oxygen is an element with atomic number 8, which means that all oxygen atoms have 8 protons in their nuclei.
When a substance is composed of only one type of atom, it is referred to as a pure element. Examples of pure elements include oxygen (O), carbon (C), gold (Au), and many others.
Furthermore, it's important to note that atoms themselves are composed of smaller particles. The three main subatomic particles are protons, neutrons, and electrons. Protons and neutrons are located in the nucleus of an atom, while electrons orbit around the nucleus. However, within a given element, all atoms have the same number of protons (atomic number), which defines the identity of the element. So, in a pure element, all the atoms are the same type.
In summary, it is indeed possible for something to be made up of only one type of atom or particle, and such substances are known as pure elements.