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

Question: 1 / 400

What does the atomic number of an element represent?

The number of neutrons in an atom

The total number of particles in an atom

The number of protons in the nucleus of an atom

The atomic number of an element is defined as the number of protons present in the nucleus of an atom. This fundamental characteristic distinguishes one element from another and determines its position on the periodic table. For example, an element with an atomic number of 6 has 6 protons in its nucleus, which identifies it as carbon.

While other options mention various aspects of atomic structure, they do not accurately describe what the atomic number represents. The number of neutrons determines isotopes of an element, the total number of particles combines protons and neutrons without specifying one or the other, and the average mass of an atom relates to both the number of protons and neutrons and the binding energy within the nucleus, not just the protons alone. Therefore, recognizing that the atomic number refers specifically to the count of protons is essential for understanding elemental identity and behavior in chemical reactions.

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The average mass of an atom

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