Which of the following is not considered a subatomic particle of an atom in basic chemistry, that is, it is not one of the fundamental particles found inside atoms?

Introduction / Context:
The structure of the atom in basic chemistry is built from subatomic particles such as protons, neutrons, and electrons. This question tests the ability to distinguish genuine subatomic particles from whole atoms or other entities. It asks which of the listed options is not a subatomic particle of an atom and therefore should not be considered part of the basic internal structure of a single atom.

Given Data / Assumptions:

• We use the simple model of the atom consisting of protons and neutrons in the nucleus and electrons in surrounding shells.
• Subatomic particles are smaller than atoms and are constituents of atoms.
• Some options may refer to elementary particles, while others may refer to entire atoms or chemical elements.
• We are working at the level of introductory general chemistry.

Concept / Approach:
Subatomic particles are the building blocks of atoms. In basic chemistry, the three main ones are the proton (positively charged, in the nucleus), neutron (neutral, in the nucleus), and electron (negatively charged, around the nucleus). Other subatomic or elementary particles exist in advanced physics, such as positrons. However, xenon is not a subatomic particle but a complete atom and a noble gas element in the periodic table. Recognising xenon as a chemical element rather than a constituent particle of an atom is the key to answering this question.

Step-by-Step Solution:

Verification / Alternative check:
To verify, think about where each entity appears in atomic structure diagrams. Protons, neutrons, and electrons are shown inside or around a nucleus. Positrons may appear in nuclear reactions or particle physics diagrams but are at the same scale as electrons. Xenon, however, is drawn as an entire atom with its own nucleus and electron cloud. Additionally, xenon appears as an entry in the periodic table, whereas subatomic particles do not. This confirms that xenon is not a subatomic particle.

Why Other Options Are Wrong:

• Neutron: A neutral subatomic particle found in the nucleus of most atoms and crucial for isotope differences.
• Electron: A negatively charged subatomic particle that occupies regions around the nucleus and determines chemical bonding.
• Proton: A positively charged subatomic particle located in the nucleus that defines the atomic number and element identity.
• Positron: The antiparticle of the electron, present in some nuclear and particle reactions, and considered a subatomic particle even though it is not part of ordinary stable atoms.

Common Pitfalls:
Learners sometimes confuse the names of elements and particles, especially when options mix both. Another common error is to assume that anything mentioned in physics contexts is a subatomic particle. Remember that chemical elements like xenon, oxygen, or iron refer to atoms or collections of atoms, while subatomic particles are smaller entities that make up the atoms. Keeping this distinction clear helps in answering similar questions correctly.

Final Answer:
The entity that is not a subatomic particle of an atom is Xenon.