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

This is because mendeleev wanted to arrange the elements not only by the increasing atomic mass but also by their similarities
When isotopes were discovered they were not able to accommodate.