Which of the following was the main defect of Dobereiner's triad?

Correct option is B

Sol: The correct answer is (b) He was unable to form triads of more than three elements.

Key Points:

• The main defect of Dobereiner's triads was that he was unable to extend his method to include all known elements.
• His classification was limited to only a few triads, as not all elements could be grouped into sets of three with similar properties and a pattern in atomic masses.
• This limitation made his system incomplete and inadequate for classifying the growing number of elements discovered at the time.​
  

Information booster:

Dobereiner's Triads:

• Definition: Dobereiner grouped elements into triads with similar properties and increasing atomic masses.
• Atomic Mass Rule: The atomic mass of the middle element is the average of the other two.
• Examples: Lithium-Sodium-Potassium, Calcium-Strontium-Barium, Chlorine-Bromine-Iodine.
• Periodic Properties: Elements in a triad show gradual changes in properties like density and reactivity.
• Limitations: Could only group a few elements; many did not fit into triads.
• Significance: Laid the foundation for the modern periodic classification of elements.