Radiation Safety Practice Exam

What is the atomic mass number?

1. The sum of protons and electrons

2. The sum of protons and neutrons in an atom

3. The number of protons in an atom

4. The total number of particles in the nucleus

The correct answer is: The sum of protons and neutrons in an atom

The atomic mass number is defined as the sum of the protons and neutrons in the nucleus of an atom. This value represents the total mass of the atom because protons and neutrons contribute significantly to the atom's overall mass, while electrons have a negligible mass in comparison. In the context of the atomic structure, the number of protons determines the element's identity, while the neutrons contribute to the mass and can affect the stability of the nucleus. As such, the atomic mass number is a crucial concept in understanding the composition of different isotopes of an element, since isotopes have the same number of protons but differ in the number of neutrons. This understanding is fundamental in various fields including chemistry, physics, and nuclear science, making it important to distinguish between the different components of an atom when discussing its characteristics.