Final answer:
The stability of an atom is primarily determined by its protons and neutrons, which are held together by the strong nuclear force, while electrons, having less mass, do not significantly contribute to the nucleus's stability and their reactivity can decrease overall stability.
Step-by-step explanation:
How do subatomic particles (protons, neutrons, and electrons) affect the stability of an atom? The correct answer is A) Protons and neutrons increase stability, while electrons decrease stability. This is because both protons and neutrons contribute to the atomic mass, and they are held together in the nucleus by the strong nuclear force. Protons have a positive electrical charge and attract the negatively charged electrons, thus contributing to the structural stability of the atom. Neutrons, being neutral, contribute to the stability by moderating the electrostatic repulsion between protons. In contrast, electrons, because of their very small mass and negative charge, do not significantly add to the mass or stability of the nucleus, and their high-speed motion can contribute to reactivity, which can be interpreted as a decrease in stability.