Question

In what order did Mendeleev arrange the elements in the periodic table?

Answer 1

In the increasing order of the atomic mass of the elements.

Explanation:

In 1869, Mendeleev suggested a classification that had the elements listed in order of increasing atomic mass, and the elements that had similar properties were regrouped in families one above each other..

The modern classification of elements orders them by increasing atomic number instead of increasing atomic mass.