rate at which the elements chemically react. hardness of the elements. structure of the atoms of the elements. radioactivity of the atoms of the elements.
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: The periodic table of the elements is systematically organized according to the
Possibilities:
- rate at which the elements chemically react.
- hardness of the elements.
- structure of the atoms of the elements.
- radioactivity of the atoms of the elements.

structure of the atoms of the elements.