Which term is defined as the number of protons in the nucleus that determines the element?

• A. Buffer
• B. Organic Compound
• C. Atomic Number
• D. Atomic Mass Number

Answer: (C)

The number of protons in the nucleus defines the element’s identity, and that count is called the atomic number. This fixed value uniquely identifies each element (for example, hydrogen has 1 proton, carbon has 6, oxygen has 8). In a neutral atom, the atomic number also equals the number of electrons, which helps determine chemical behavior. Isotopes differ in the number of neutrons, which changes mass but not the element itself because the protons (the atomic number) stay the same. The other terms aren’t about proton count: a buffer relates to pH stability, an organic compound is a carbon-based molecule class, and the atomic mass number equals protons plus neutrons, not just protons.