Which fundamental property is primarily responsible for the periodicity observed in the periodic table?

• A. The chemical reactivity of elements with oxygen
• B. The increasing atomic mass of elements
• C. The repeating pattern of electron configurations as atomic number increases
• D. The arrangement of elements by their physical state (solid, liquid, gas)

Answer: (C)

Verified step by step guidance

1. Understand that the periodicity in the periodic table refers to the recurring trends or patterns in the properties of elements as you move across or down the table.
2. Recognize that these patterns arise because elements are arranged in order of increasing atomic number, which corresponds to the number of protons in the nucleus.
3. Know that the electron configuration of an element describes the distribution of electrons in its atomic orbitals, and this configuration repeats in a predictable way as atomic number increases.
4. Realize that the repeating electron configurations lead to similar chemical properties at regular intervals, which is the fundamental reason for the periodic trends observed.
5. Conclude that the primary property responsible for periodicity is the repeating pattern of electron configurations as atomic number increases, rather than atomic mass, physical state, or specific chemical reactivity.