Which of the following best describes Johann Döbereiner's contribution to the development of the periodic table?

• A. He proposed the law of octaves, grouping elements by repeating properties every eighth element.
• B. He grouped elements into triads based on similar chemical properties and atomic masses.
• C. He arranged elements in order of increasing atomic number.
• D. He discovered the noble gases and added a new group to the periodic table.

Answer: (B)

Verified step by step guidance

1. Understand the historical context of the periodic table development and the contributions of various scientists.
2. Recall that Johann Döbereiner is known for identifying groups of three elements, called triads, which have similar chemical properties and show a relationship in their atomic masses.
3. Recognize that Döbereiner's triads were an early attempt to classify elements based on their properties and atomic masses before the modern periodic table was developed.
4. Compare Döbereiner's work with other contributions: the law of octaves was proposed by Newlands, arranging by atomic number was done by Moseley, and the discovery of noble gases was by Ramsay.
5. Conclude that Döbereiner's key contribution was grouping elements into triads based on similar chemical properties and atomic masses.