The atomic number of an element is derived from

Options

A. Number of electrons
B. Number of protons
C. Number of neutrons
D. Number of nucleons

Explanation

**Step-by-Step Solution:**

1. **Understanding Atomic Number**: The atomic number (Z) of an element is a fundamental property that defines the element. It is represented by the letter Z in the periodic table.

2. **Definition of Atomic Number**: The atomic number is defined as the number of protons present in the nucleus of an atom of that element. For example, sodium (Na) has an atomic number of 11, which means it has 11 protons.

3. **Protons vs. Electrons**: In a neutral atom, the number of protons is equal to the number of electrons. However, when the atom becomes an ion (either cation or anion), the number of electrons can change, but the number of protons remains constant.

4. **Example with Sodium**: When sodium (Na) is in its elemental state, it has 11 protons and 11 electrons. If sodium loses an electron to form a cation (Na⁺), it will have 11 protons and 10 electrons. Despite this change in electron count, the atomic number (which is based on protons) remains 11.

5. **Conclusion**: Therefore, the atomic number of an element is derived from the number of protons in its nucleus. It cannot be derived from the number of neutrons or electrons, as those can vary in ionic forms or isotopes.

**Final Answer**: The atomic number of an element is derived from the number of protons.

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