Question

According to the law of triad:
A.the properties of the middle element were in between those of the other two members.
B.three elements arranged according to increasing weights have similar properties.
C.the elements can be grouped in groups of six elements.
D.every third element resembles the first element in the periodic table.

Answer 1

Hint: A triad is the grouping of three elements in order of some property common to all the three elements. And these elements form some relation among themselves relating to that property.

Complete step by step answer:
- The law of Triads was given by the German chemist Johann Wolfgang Dobereiner. He identified that there were groups of elements that showed similar properties.
- He observed that the group of three elements, known as triads, could be formed in which all the three elements shared similar physical properties and chemical properties.
- A triad is a grouping of three elements in order of their atomic masses. Dobereiner started his law of Triads as, "The arithmetic mean of the atomic masses of the first and the third element would approximately be equal to the atomic mass of the second element in that triad."
- He suggested that this law can also extend to other properties of the elements such as density. In 1817, the first Dobereine's Triad was identified and it constituted of the alkaline earth metals calcium, strontium and barium.
- In this, the arithmetic mean of the atomic masses of barium and calcium is equal to the atomic mass of strontium.

Therefore, according to the law of triads, the properties of the middle element were in between those of the other two members. Hence, the correct answer is option (A).

Note: There are some limitations of this law:
-This method eventually became obsolete with the identification of new elements.
-The newly identified elements did not fit into the triads.
-Only a total of 5 Dobereiner's triad were identified.
-Even most of the known elements did not fit into triads.