How many groups are there in Mendeleev's Periodic Classification? 

8

The correct answer is option 2. 8.

Dmitri Mendeleev's Periodic Table, proposed in 1869, was one of the early attempts to organize the known chemical elements based on their properties. Mendeleev organized the elements in increasing order of their atomic masses and noticed that elements with similar properties occurred at regular intervals. He arranged the elements into rows and columns, creating a table.

In Mendeleev's original classification, there were eight vertical columns, which he called groups. These groups were organized based on the observed chemical properties of the elements. The elements within each group had similar chemical behaviors, and there was a periodic repetition of properties across the table.

Mendeleev left gaps in his table for undiscovered elements and even predicted the properties of some of these missing elements. His predictions were later validated when those elements were discovered, providing strong support for the periodic law.

While Mendeleev's table laid the foundation for the modern periodic table, there have been refinements and adjustments over time. The modern periodic table, developed based on atomic numbers rather than atomic masses, retains the concept of groups, and elements within the same group generally exhibit similar chemical properties.