Question

At the time of Mendeleev ______ elements were known.

Options

• 56

• 65

• 63

• 118

Answer 1

At the time of Mendeleev 63 elements were known.

Explanation:

At the time when Dmitri Mendeleev began his work on the periodic classification of elements, 63 elements were known. He based his periodic table on the atomic masses of these elements and their chemical properties, specifically focusing on the formation of oxides and hydrides.