The fact which helped in developing Moseley's table was that the number of protons in an atom is different than the atom's total mass. Thus, the correct option is C.
Mendeleev's periodic table can be defined as a systematic positioning of chemical elements on the basis of their increasing atomic mass in a tabular form. It reflects the similarities and the trends in the behavior of these elements.
Mendeleev's periodic table helped Moseley in developing the periodic table to a major extent. As, all the drawbacks of Mendeleev's periodic table are shorted out by Moseley in a more efficient way.
One of the drawbacks which was shorted out was the number of protons in an atom is different than the atom’s total mass because the total atomic mass of a chemical element depends on the number of protons in the element, neutrons, and electrons. Altogether, these constitute the element.
Therefore, the correct option is C.
Learn more about Mendeleev's Periodic table here:
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