Why was Moseley able to resolve the discrepancies in Mendeleev's table when mendeleev could not?

Answer 1

Mendeleev only had mass as a criterion to order by. Hence the anomalies.

Moseley used x-ray wavelengths, which depend directly on the energy of interaction of electrons with the nucleus, and hence with nuclear charge.

See Henry Moseley and Moseley's Law, Wikipedia.

Answer 2

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