Q8 of 60 Page 140

Doberiener’s system of classification into triads was not found to be useful as he could identify only:

He could only find 3 triads in elements due to this his concept was discarded.

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6

When Mendeleev started his work, the number of known elements was:

 7

It was assumed by Newlands that only:

 9

It was found that the law of octaves was applicable only to:

 10

The element X has the following electron configuration 2, 8, 8, 2. It means that it belongs to: