Question

Q1)What do A and B represent in Mendeleev's periodic table?
Q2)In​Mendeleev'speriodic table, the atomic masees do not increase in a regular manner in going from one element to the next. How does it create a problem to predict new elements?

Answer 1

Q1). Answer is here
There are eight groups in each periodic table and two sub groups , A and B Lanthanide and Actinides .

Answer 2

Explanation:

The dividing of groups into subgroups was felt necessary because many elements which doesn't have similar properties came under same group.

So like this group I was divided into IA and IB ; group II was divided into IIA and IIB and so on till group VII

for example take K and Cu..where these r in same group 1 and period 4 as they match with their hybrides and oxide formulae but have different properties ie alkali metal and transition metal