Question

how did moseley establish a more accurate periodic table?
by arranging the elements according to atomic mass instead of atomic number
by arranging the elements according to atomic number instead of atomic mass
by arranging the elements into horizontal periods
by arranging the elements into vertical groups

Explanation:

Moseley's contribution to the periodic table was based on the concept of atomic number (the number of protons in an atom's nucleus). Previously, Mendeleev arranged elements by atomic mass, but this led to some inconsistencies (e.g., elements like iodine and tellurium were out of order when arranged by atomic mass). Moseley used X - ray spectroscopy to determine the atomic number of elements and found that arranging elements by atomic number (instead of atomic mass) resolved these inconsistencies and created a more accurate periodic table. The options about horizontal periods and vertical groups were already part of Mendeleev's periodic table, and the option about arranging by atomic mass is incorrect as that was the older, less accurate method.

Answer:

B. by arranging the elements according to atomic number instead of atomic mass