The Mendeleev and Mosley periodic charts have gaps for the as-then-undiscovered elements. Why do you think the chart used by Mosley was more accurate at predicting where new elements would be placed?

Moseley arranged the elements in order of their atomic number

Explanation:

Mendeleev arranged the elements in order of their atomic mass.

His table had gaps for the then-unknown elements, but it also had problems, because Co and Ni were out of order and so were Te and I.

The noble gases, most of the lanthanides and actinides, and none of the trans-uranium elements had then been discovered.

When Moseley arranged the elements according to their atomic numbers, the Ni-Co and Te-I anomalies disappeared.

The modern arrangement shows the elements unknown to Mendeleev highlighted in pink.

Using Moseley's chart based on atomic number, it became much easier for scientists to put newly-discovered elements in their correct places in the Periodic Table.

the answer would be a

the answer is na (sodium)