Question

3.

(a) What was the basis of classification of elements by Dobereiner? Why was it discarded?

(b State modern periodic law. State any one defect of Mendeleeff’s periodic table and any one contribution

of Mendeleef.

(c) An element is having atomic number 12. Find out the period and group to which it belongs.

(d) Name the following :

(i) The group whose elements have zero valency.

(ii) The name of the elements belonging between group III A to VII A ​

Answer 1

Answer:

Only three triads could be formed and was not holding for other elements. The law was not applicable even in the same family