ACS Chemistry Practice Exam 2025 – The All-in-One Guide to Exam Success!

An alpha particle is composed of two protons and two neutrons. This specific arrangement reflects the structure of a helium nucleus, as an alpha particle can be considered a helium-4 nucleus. Being made up of two protons gives the alpha particle a positive charge, while the presence of two neutrons contributes to its mass without adding to the overall charge. The properties of alpha particles play a critical role in nuclear chemistry and radioactivity, particularly in alpha decay processes where heavy nuclei emit these particles to achieve greater stability.

The other options presented do not reflect the actual composition of an alpha particle. For instance, including electrons in any option is not accurate, as alpha particles do not contain electrons; they are charged particles, not atoms. The presence of neutrons without protons does not form a stable particle, while a combination of four protons and neutrons overshoots the nuclear structure of an alpha particle, which specifically has a total mass number of 4 (2 protons + 2 neutrons).