**Explanation:**

A pure substance is a material that is composed of only one type of particle. These particles can be atoms, molecules, or ions.

- **Atoms:** Atoms are the smallest units of elements. They are composed of protons, neutrons, and electrons. Each element is made up of a unique type of atom. For example, oxygen is made up of oxygen atoms (O), carbon is made up of carbon atoms (C), and so on.

- **Molecules:** Molecules are composed of two or more atoms chemically bonded together. These atoms can be of the same element or different elements. For example, oxygen gas (O2) is composed of two oxygen atoms bonded together, while water (H2O) is composed of two hydrogen atoms bonded to one oxygen atom.

- **Ions:** Ions are charged particles that are formed when atoms gain or lose electrons. They can be positive ions (cations) or negative ions (anions). For example, sodium chloride (NaCl) is composed of sodium ions (Na+) and chloride ions (Cl-).

A pure substance consists of only one type of these particles. It means that all the particles in a pure substance are identical in their chemical composition and properties. They cannot be separated into different components by physical means, such as filtration or evaporation.

On the other hand, a mixture contains two or more different types of particles. These particles can be physically separated from each other using various methods such as filtration, distillation, or chromatography. A mixture can be homogeneous (uniform composition throughout) or heterogeneous (non-uniform composition).

Therefore, the correct answer is option B: A pure substance/element contains one type of particles.

The correct answer is option B because elements are made up of only one kind of particles. Hope it will help you!!!!