What pattern did Mendeleev discover when he arranged the elements in the periodic table?

• A. Elements show periodic repetition of chemical and physical properties when arranged by increasing atomic mass.
• B. Elements are organized based on their density.
• C. Elements with similar melting points are placed together.
• D. Elements are grouped by their color when arranged in order.

Answer: (A)

Verified step by step guidance

1. Understand that Dmitri Mendeleev arranged the elements in order of increasing atomic mass.
2. Observe that when elements are arranged this way, certain chemical and physical properties repeat at regular intervals.
3. Recognize that this repetition of properties is called periodicity, which means properties recur periodically as atomic mass increases.
4. Note that Mendeleev used this pattern to group elements with similar properties into columns (groups) in his periodic table.
5. Conclude that the key pattern Mendeleev discovered is the periodic repetition of chemical and physical properties when elements are arranged by increasing atomic mass.