Answer:
was difficult to place isotopes of elements as they have the same chemical properties but different atomic masses. It was not possible to predict how many elements could be discovered between two heavy elements as the rise in atomic mass is not uniform.
The three obstacles that Mendeleev faced in his life include the following:
Mendeleev was of Russian region and was instrumental in the formation of
the periodic law and table. He faced several challenges such as marital
issues and also in the formulation of the periodic table as it became
ambiguous for him.
He couldn't fit in some elements on the table due to differences in the order
of atomic masses .
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