Question

Discovery of which species posed a great challenged to Mendeleev's periodic
classification of elements?
Isobars
Isotopes
Isotones
Isotherms​

Answer 1

Answer:

In his 1869 Periodic Table, Mendeleev left blanks with suggested atomic weights for elements he thought would be discovered someday. William Ramsay's discovery of argon initially posed a threat to the Periodic Table.

Answer 2

Answer: ISOTOPES..

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