Algonquin College Health Program Assessment (AC-HPAT) Practice Exam

What does the mass number represent?

1. The total number of protons and electrons

2. The sum of protons and neutrons in the nucleus

3. The average of all isotopes of an element

4. The total number of protons and electrons minus neutrons

The correct answer is: The sum of protons and neutrons in the nucleus

The mass number is a significant concept in understanding atomic structure, specifically representing the total count of protons and neutrons within the atomic nucleus. Protons have a positive charge, while neutrons are neutral, and collectively they determine the mass of an atom, as electrons have negligible mass compared to protons and neutrons. By summing the number of protons (which defines the element and is equal to the atomic number) and neutrons, the mass number provides insight into the atomic mass of an isotope of an element. This is fundamental in various fields of science, including chemistry, physics, and biology, as it helps in identifying isotopes, understanding nuclear reactions, and predicting the behavior of elements in chemical reactions. Other options do not accurately describe the mass number. While one option mentions the total number of protons and electrons, it neglects neutrons entirely, which are crucial to determining the mass. Another option suggests calculating an average of isotopes, which relates more closely to atomic weight rather than mass number, and the last option incorrectly implies a subtraction that does not reflect the components contributing to mass. Thus, understanding that the mass number is the sum of protons and neutrons is essential for grasping atomic properties and behavior.