Question

state the merits of Mendeleev classification of element

Answer 1

=> systematic study of elements
=>correction of atomic masses
=>position of noble gases
=> Mendeleev predicated the properties of those missing elements from the known properties of the other elements in the same group

Answer 2

He could predict errors of the elements.
He could also predict the properties of the elements which was not discovered at that time.
He left blank spaces for the future so that if elements were discovered, if could fit in it.

Hope this helps!!