According to Dobereiner, ___________.

Correct option is B

Correct Answer: (b) The arithmetical mean of the atomic masses of the first and the third element of the triad is equal to that of the second one

Explanation:

• According to Dobereiner's Law of Triads, when elements are grouped into sets of three (called triads) based on their similar chemical properties, the atomic mass of the middle element is approximately the arithmetic mean of the atomic masses of the first and the third elements.

For example:

• In the triad of Lithium (Li), Sodium (Na), and Potassium (K): 

• 

• 
  

This relationship helped Dobereiner identify patterns in the properties of elements before the development of the periodic table.