ACS Chemistry Practice Exam 2026 – The All-in-One Guide to Exam Success!

Neutrons are subatomic particles that reside within the atomic nucleus alongside protons. The primary function of neutrons is to contribute to the overall mass of an atom. The mass number of an atom is calculated by adding the number of protons and neutrons together. Therefore, neutrons play a crucial role in determining the mass number, which reflects the total count of the nucleons (protons and neutrons) in the nucleus.

Other statements do not accurately describe the nature of neutrons. Neutrons are electrically neutral, meaning they carry no charge, which directly contradicts the claim about them being positively charged. Additionally, it is the electrons, which surround the nucleus, that primarily influence the chemical properties of an atom, rather than neutrons or protons. Lastly, neutrons are firmly located within the nucleus; they are not found outside of it. This solidifies the significance of neutrons in contributing to the mass number as the only accurate statement among the options provided.