What discovery occurred after mendeleev’s periodic table was published that allowed moseley to improve it?

Revised Mendeleev's periodic table.Realized that the Atomic Mass was not as important in organizing the elements as the atomic number

Explanation:

Comparison between Mendeleev's and Moseley periodic table follows:

Mendeleev's periodic table:Mendeleev added elements in columns by the way they reacted.Mendeleev left those spaces blank in his periodic table which he believes were undiscovered elements.Mendeleev arranges the elements according to increasing Atomic weight.

    2. Moseley's periodic table:

Moseley arranged the elements according to increasing Atomic number.Moseley revised Mendeleev's periodic table and developed a new understanding of periodic law.Moseley realized that the Atomic Mass was not as important in organizing the elements as the atomic number.

Mgo2 is the oxidation state of manganese oxide

The mass has escaped into a gas which you can not see so the law stays true.