What is the fundamental organizing principle of the periodic table?

• A. Elements are arranged by increasing atomic mass
• B. Elements are organized based on their physical state at room temperature
• C. Elements are grouped according to their chemical reactivity
• D. Elements are arranged in order of increasing atomic number

Answer: (D)

Verified step by step guidance

1. Understand that the periodic table is a systematic arrangement of elements that reflects their properties and relationships.
2. Recall that early versions of the periodic table were arranged by increasing atomic mass, but this led to inconsistencies in element placement.
3. Recognize that the modern periodic table is organized by increasing atomic number, which is the number of protons in an atom's nucleus.
4. Know that arranging elements by atomic number aligns elements with similar chemical properties into groups (columns), showing periodic trends.
5. Conclude that the fundamental organizing principle of the periodic table is the arrangement of elements in order of increasing atomic number.