Which term is defined as the sum of protons and neutrons in an atom?

• A. Isotopic mass
• B. Mass number
• C. Atomic mass
• D. Atomic number

Answer: (B)

Verified step by step guidance

1. Understand the structure of an atom: An atom consists of protons, neutrons, and electrons. Protons and neutrons are located in the nucleus, while electrons orbit around the nucleus.
2. Define the term 'mass number': The mass number is the total count of protons and neutrons in the nucleus of an atom. It is a whole number and is specific to each isotope of an element.
3. Differentiate between related terms: The atomic number is the number of protons in the nucleus of an atom, which defines the element. The atomic mass is the weighted average mass of all isotopes of an element, usually expressed in atomic mass units (amu). Isotopic mass refers to the mass of a specific isotope of an element.
4. Recognize the correct term: The sum of protons and neutrons in an atom is specifically referred to as the 'mass number'.
5. Apply this knowledge: When asked for the sum of protons and neutrons, identify it as the mass number, not to be confused with atomic mass or atomic number.