Question

How many elements were known at the time of dobereiner?

Answer 1

Hi !

During the attempts by Dobereiner , for classifying elements , less than 33 elements were known at the time.
He arranged the elements in increasing order of atomic no:s.
He arranged the elements into groups , with three elements each , in it.
The atomic mass of the element in between the other two , in the group , had the atomic mass equal to the average of the other two.

Answer 2

Answer:

38 element existed because in his table strontium existed which is the last element hence 38 element were known during dobreiner started his research