Question

Atomic number of an element is equal to the:

• A. Number of electrons
• B. Number of neutrons
• C. Number of protons
• D. Total number of protons and neutrons

Hint:

Atomic number is defined by the nucleus, specifically its positive charge.

Answer 1

The Correct Option is C

Step 1: Recall the definition.
The atomic number (Z) of an element is defined as the number of protons present in the nucleus of an atom.
Step 2: Why protons and not electrons.
In a neutral atom the number of electrons equals the number of protons, but in an ion these two numbers differ, while the atomic number always stays fixed at the proton count. So protons, not electrons, define atomic number.
Step 3: Why not neutrons or total nucleons.
The number of neutrons can vary between isotopes of the same element without changing its identity, so neutrons alone cannot define atomic number. The sum of protons and neutrons is called the mass number, a separate quantity.
Final Answer: C) Number of protons.