Question

1. which of the following best explains why mendeleevs periodic table was organized according to atomic mass rather than atomic number, like modern periodic tables? atomic number is more closely related to reactivity atomic number had not yet been discovered. atomic mass varies among the isotopes of an element. atomic mass is unaffected by chemical reactions

Explanation:

Mendeleev created his periodic table in the 19th century. At that time, the concept of atomic number (which is related to the number of protons in an atom) had not been discovered. Scientists knew about atomic masses from chemical experiments and mass - related properties. So, he used atomic mass as the organizing principle.

Answer:

Atomic number had not yet been discovered.