Question

Example of Dobereiner’s triad is ___________.
A. Li, Al, Ca
B. Li, Na, K
C. Li, K, Na
D. K, Al, Ca

Answer 1

Hint: We know that before constructing the modern periodic table, there were many attempts to classify elements. Among them, Dobereiner’s triads, Newlands law of octaves, is important.

Complete step by step answer:
First we discuss Dobereiner's triads. Law of triads was given by a German scientist whose name is Johann Wolfgang Dobereiner. He observed that the group of three elements could be constituted where all the elements possess similar properties (chemical and physical). According to the law of Dobereiner, the arithmetic mean of the third and first element of the triad is equal to the second element's atomic mass. The triads identified by him was,
Triad 1- Lithium (Li), sodium (Na), potassium (K)
Triad 2-Calcium (Ca), strontium (Sr) , barium (Ba)
Triad 3-Chlorine (Cl), bromine (Br), iodine (I)
Triad 4-Sulphur (S), selenium (Se), tellurium (Te)
Triad 5-Iron (I), Cobalt (Co), nickel (Ni)
Hence, the correct answer is B.

Additional Information: Newlands law of octaves was one among the early attempts made to group elements considering their properties. According to the law of octaves by Newland, every eight elements possess similar properties on arranging elements following the order of increasing atomic mass. There are many defects of Newlands law such as his classification was successful up to element calcium. After that every eighth element does possess similar properties to the first element.

Note: The triads discovered by Dobereiner helped in classification of elements of similar characteristics together but the drawback is that he was unable to group all the elements known at that time into triads. Therefore, this triad could not gain much importance.